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Isotopomers
Isotopomers or isotopic isomers are isomers which differ by isotopic substitution, and which have the same number of atoms of each isotope but in a different arrangement. For example, CH3OD and CH2DOH are two isotopomers of monodeuterated methanol. The molecules may be either structural isomers (constitutional isomers) or stereoisomers depending on the location of the isotopes. Isotopomers have applications in areas including nuclear magnetic resonance spectroscopy, reaction kinetics, and biochemistry. Description Isotopomers or isotopic isomers are isomers with isotopic atoms, having the same number of each isotope of each element but differing in their positions in the molecule. The result is that the molecules are either constitutional isomers or stereoisomers solely based on isotopic location. The term isotopomer was first proposed by Seeman and Paine in 1992 to distinguish isotopic isomers from isotopologues (isotopic homologues). Examples * CH3CHDCH3 and CH3CH2CH2D ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the existence or possibility of isomers. Isomers do not necessarily share similar chemical property, chemical or physical property, physical properties. Two main forms of isomerism are structural isomerism, structural (or constitutional) isomerism, in which ''chemical bond, bonds'' between the atoms differ; and stereoisomerism (or spatial isomerism), in which the bonds are the same but the ''relative positions'' of the atoms differ. Isomeric relationships form a hierarchy. Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different Isotopologue, isotopologues. The depth of analy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotopologue
In chemistry, isotopologues (also spelled isotopologs) are molecules that differ only in their isotopic composition. They have the same chemical formula and bonding arrangement of atoms, but at least one atom has a different number of neutrons than the parent. An example is water, whose hydrogen-related isotopologues are: "light water" (HOH or ), " semi-heavy water" with the deuterium isotope in equal proportion to protium (HDO or ), "heavy water" with two deuterium atoms ( or ); and "super-heavy water" or tritiated water ( or , as well as and , where some or all of the hydrogen is the radioactive tritium isotope). Oxygen-related isotopologues of water include the commonly available form of heavy-oxygen water () and the more difficult to separate version with the isotope. Both elements may be replaced by isotopes, for example in the doubly labeled water isotopologue . Altogether, there are 9 different stable water isotopologues, and 9 radioactive isotopologues involving tr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PSIA Wiki1 , the national intelligence agency of Japan
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PSIA or psia may refer to: * Physical Security Interoperability Alliance, industrial standardization initiative promoting interoperability of IP-enabled security devices * Pounds per square inch absolute (including atmospheric pressure) * Professional Ski Instructors of America, an organization offering training and certification for U.S. Ski Instructors * Philippine Software Industry Association * Paris School of International Affairs * Private Schools Interscholastic Association * Palm Springs International Airport * Public Security Intelligence Agency The is the Security agency, domestic intelligence agency of Japan. It is administered by the Ministry of Justice (Japan), Ministry of Justice and is tasked with internal security and espionage against threats to Japanese national security based o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Potato
The potato () is a starchy tuberous vegetable native to the Americas that is consumed as a staple food in many parts of the world. Potatoes are underground stem tubers of the plant ''Solanum tuberosum'', a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern United States to southern Chile. Genetic studies show that the cultivated potato has a single origin, in the area of present-day southern Peru and extreme northwestern Bolivia. Potatoes were domesticated there about 7,000–10,000 years ago from a species in the '' S. brevicaule'' complex. Many varieties of the potato are cultivated in the Andes region of South America, where the species is indigenous. The Spanish introduced potatoes to Europe in the second half of the 16th century from the Americas. They are a staple food in many parts of the world and an integral part of much of the world's food supply. Following millennia of selective breeding, there are now over 5 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dicotyledon
The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, that the seed has two embryonic leaves or cotyledons. There are around 200,000 species within this group. The other group of flowering plants were called monocotyledons (or monocots), typically each having one cotyledon. Historically, these two groups formed the two divisions of the flowering plants. Largely from the 1990s onwards, molecular phylogenetic research confirmed what had already been suspected: that dicotyledons are not a group made up of all the descendants of a common ancestor (i.e., they are not a monophyletic group). Rather, a number of lineages, such as the magnoliids and groups now collectively known as the basal angiosperms, diverged earlier than the monocots did; in other words, monocots evolved from within the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rice
Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much less commonly, ''Oryza glaberrima'' (African rice). Asian rice was domesticated in China some 13,500 to 8,200 years ago; African rice was domesticated in Africa about 3,000 years ago. Rice has become commonplace in many cultures worldwide; in 2023, 800 million tons were produced, placing it third after sugarcane and maize. Only some 8% of rice is traded internationally. China, India, and Indonesia are the largest consumers of rice. A substantial amount of the rice produced in developing nations is lost after harvest through factors such as poor transport and storage. Rice yields can be reduced by pests including insects, rodents, and birds, as well as by weeds, and by List of rice diseases, diseases such as rice blast. Traditional rice polyc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monocotyledon
Monocotyledons (), commonly referred to as monocots, ( Lilianae '' sensu'' Chase & Reveal) are flowering plants whose seeds contain only one embryonic leaf, or cotyledon. A monocot taxon has been in use for several decades, but with various ranks and under several different names. The APG IV system recognises its monophyly but does not assign it to a taxonomic rank, and instead uses the term "monocots" to refer to the group. Monocotyledons are contrasted with the dicotyledons, which have two cotyledons. Unlike the monocots however, the dicots are not monophyletic and the two cotyledons are instead the ancestral characteristic of all flowering plants. Botanists now classify dicots into the eudicots ("true dicots") and several basal lineages from which the monocots emerged. The monocots are extremely important economically, culturally, and ecologically, and make up a majority of plant biomass used in agriculture. Common crops such as dates, onions, garlic, rice, wheat, maize, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon Dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at normally-encountered concentrations it is odorless. As the source of carbon in the carbon cycle, atmospheric is the primary carbon source for life on Earth. In the air, carbon dioxide is transparent to visible light but absorbs infrared, infrared radiation, acting as a greenhouse gas. Carbon dioxide is soluble in water and is found in groundwater, lakes, ice caps, and seawater. It is a trace gas Carbon dioxide in Earth's atmosphere, in Earth's atmosphere at 421 parts per million (ppm), or about 0.042% (as of May 2022) having risen from pre-industrial levels of 280 ppm or about 0.028%. Burning fossil fuels is the main cause of these increased concentrations, which are the primary cause of climate change.IPCC (2022Summary for pol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paleolithic
The Paleolithic or Palaeolithic ( years ago) ( ), also called the Old Stone Age (), is a period in human prehistory that is distinguished by the original development of stone tools, and which represents almost the entire period of human prehistoric technology. It extends from the earliest known use of stone tools by Hominini, hominins, 3.3 million years ago, to the end of the Pleistocene, 11,650 Before Present#Radiocarbon calibration, cal Before Present, BP. The Paleolithic Age in Europe preceded the Mesolithic Age, although the date of the transition varies geographically by several thousand years. During the Paleolithic Age, hominins grouped together in small societies such as band society, bands and subsisted by gathering plants, fishing, and hunting or scavenging wild animals. The Paleolithic Age is characterized by the use of Knapping, knapped stone tools, although at the time humans also used wood and bone tools. Other organic commodities were adapted for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kinetic Isotope Effect
In physical organic chemistry, a kinetic isotope effect (KIE) is the change in the reaction rate of a chemical reaction when one of the atoms in the reactants is replaced by one of its isotopes. Formally, it is the ratio of rate constants for the reactions involving the light (''k'') and the heavy (''k'') isotopically substituted reactants ( isotopologues): KIE = ''k/k''. This change in reaction rate is a quantum effect that occurs mainly because heavier isotopologues have lower vibrational frequencies than their lighter counterparts. In most cases, this implies a greater energy input needed for heavier isotopologues to reach the transition state (or, in rare cases, dissociation limit), and therefore, a slower reaction rate. The study of KIEs can help elucidate reaction mechanisms, and is occasionally exploited in drug development to improve unfavorable pharmacokinetics by protecting metabolically vulnerable C-H bonds. Background KIE is considered one of the most essential ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
INADEQUATE
Two-Dimensional Nuclear Magnetic Resonance (2D NMR) is an advanced spectroscopic technique that builds upon the capabilities of one-dimensional (1D) NMR by incorporating an additional frequency dimension. This extension allows for a more comprehensive analysis of molecular structures. In 2D NMR, signals are distributed across two frequency axes, providing improved resolution and separation of overlapping peaks, particularly beneficial for studying complex molecules. This technique identifies correlations between different nuclei within a molecule, facilitating the determination of connectivity, spatial proximity, and dynamic interactions. 2D NMR encompasses a variety of experiments, including COSY (Correlation Spectroscopy), TOCSY (Total Correlation Spectroscopy), NOESY (Nuclear Overhauser Effect Spectroscopy), and HSQC (Heteronuclear Single Quantum Coherence). These techniques are indispensable in fields such as structural biology, where they are pivotal in determining protein ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
J-coupling
In nuclear chemistry and nuclear physics, ''J''-couplings (also called spin-spin coupling or indirect dipole–dipole coupling) are mediated through chemical bonds connecting two spins. It is an indirect interaction between two nuclear spins that arises from hyperfine interactions between the nuclei and local electrons. In NMR spectroscopy, ''J''-coupling contains information about relative bond distances and angles. Most importantly, ''J''-coupling provides information on the connectivity of chemical bonds. It is responsible for the often complex splitting of resonance lines in the NMR spectra of fairly simple molecules. ''J''-coupling is a frequency ''difference'' that is not affected by the strength of the magnetic field, so is always stated in Hz. Vector model and manifestations for chemical structure assignments The origin of ''J''-coupling can be visualized by a vector model for a simple molecule such as hydrogen fluoride (HF). In HF, the two nuclei have spin . Four st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
