1.
Hydrogen bond
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Hydrogen bonds can occur between molecules or within different parts of a single molecule. Depending on geometry and environment, the hydrogen bond free energy content is between 1 and 5 kcal/mol and this makes it stronger than a van der Waals interaction, but weaker than covalent or ionic bonds. This type of bond can occur in molecules such as water and in organic molecules like DNA. Intermolecular hydrogen bonding is responsible for the boiling point of water compared to the other group 16 hydrides that have much weaker hydrogen bonds. Intramolecular hydrogen bonding is responsible for the secondary and tertiary structures of proteins. It also plays an important role in the structure of polymers, in 2011, an IUPAC Task Group recommended a modern evidence-based definition of hydrogen bonding, which was published in the IUPAC journal Pure and Applied Chemistry. An accompanying detailed technical report provides the rationale behind the new definition, a hydrogen atom attached to a relatively electronegative atom will play the role of the hydrogen bond donor. This electronegative atom is usually fluorine, oxygen, or nitrogen, a hydrogen attached to carbon can also participate in hydrogen bonding when the carbon atom is bound to electronegative atoms, as is the case in chloroform, CHCl3. An example of a hydrogen donor is the hydrogen from the hydroxyl group of ethanol. In a hydrogen bond, the electronegative atom not covalently attached to the hydrogen is named proton acceptor, because of the small size of hydrogen relative to other atoms and molecules, the resulting charge, though only partial, represents a large charge density. A hydrogen bond results when this positive charge density attracts a lone pair of electrons on another heteroatom. The hydrogen bond is described as an electrostatic dipole-dipole interaction. These covalent features are more substantial when acceptors bind hydrogens from more electronegative donors, the partially covalent nature of a hydrogen bond raises the following questions, To which molecule or atom does the hydrogen nucleus belong. And Which should be labeled donor and which acceptor, liquids that display hydrogen bonding are called associated liquids. Hydrogen bonds can vary in strength from weak to extremely strong. For example, the central interresidue N−H···N hydrogen bond between guanine and cytosine is much stronger in comparison to the N−H···N bond between the adenine-thymine pair, the length of hydrogen bonds depends on bond strength, temperature, and pressure. The bond strength itself is dependent on temperature, pressure, bond angle, the typical length of a hydrogen bond in water is 197 pm. The ideal bond angle depends on the nature of the hydrogen bond donor, moore and Winmill used the hydrogen bond to account for the fact that trimethylammonium hydroxide is a weaker base than tetramethylammonium hydroxide
2.
Water cluster
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In chemistry a water cluster is a discrete hydrogen bonded assembly or cluster of molecules of water. These clusters have been found experimentally or predicted in silico in various forms of water, in ice, in crystal lattices and in liquid water. Shu et al. reported the images of water clusters of 100 micrometres, water clusters are also implicated in the stabilization of certain supramolecular structures. So little is understood about water clusters in bulk water that it is considered one of the problems in chemistry. In-silico, cyclic water clusters n are found with n =3 to 60, structures of water molecules with the highest resolution have been demonstrated in the studies of Richard Saykally of Berkeley College of Chemistry. Many isomeric forms seem to exist for the hexamer, from ring, book, bag, cage, two cage-like isomers exist for heptamers, and octamers are found either cyclic or in the shape of a cube. Even larger clusters are predicted, the fullerene-like cluster 28 is called the water buckyball, the 280 molecule icosahedral structure, which is 3 nm in diameter, consists of icosahedral shells with 280,100 and 20 molecules. There is increased stability with the addition of each shell, a look at the recent scientific literature may reveal good reviews on the studies of water clusters employing ab initio methods. These clusters are important for studying hydration phenomena at molecular level since they form the basic building blocks of the hydrated clusters. There are theoretical models of water clusters of more than 700 water molecules by Martin Chaplin and they have not been proven experimentally. Shu et al. observed water clusters under microscope, the experiments were conducted in two ways. One is making sodium chloride solutions and sampling water clusters from the solution and put the solution with water clusters on a glass slide under a microscope. The second method is to put a drop of Milli Q water on a slide under a microscope. Under the microscope salt starts to dissolve and break into smaller salt particles, some of the salt particles enter water clusters and reveals the appearance of water clusters. The experimental observation of water clusters requires sophisticated spectroscopic tools such as Far-infrared vibration-rotation-tunneling spectroscopy, experiments combining IR spectroscopy with mass spectrometry reveal cubic configurations for clusters in the range W8-W10. When the water is part of a structure as in a hydrate. According to the so-called in silico method quantum cluster equilibrium theory of liquids W8 clusters dominate the liquid water bulk phase followed by W5, in order to facilitate a water triple point the presence of a W24 cluster is invoked. In another model bulk water is built up from a mixture of hexamer and pentamer rings containing cavities capable of enclosing small solutes, in yet another model an equilibrium exists between a cubic water octamer and two cyclic tetramers
3.
Chemical Abstracts Service
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Chemical Abstracts Service is a division of the American Chemical Society. It is a source of chemical information, CAS is located in Columbus, Ohio, United States. Chemical Abstracts is an index that provides summaries and indexes of disclosures in recently published scientific documents. Chemical Abstracts ceased print publication on January 1,2010, the two principal databases that support the different products are CAplus and Registry. Registry contains information on more than 71 million organic and inorganic substances, the sequence information comes from CAS and GenBank, produced by the National Institutes of Health. CAS databases are available via two principal database systems, STN, and SciFinder, STN International is operated jointly by CAS and FIZ Karlsruhe, and is intended primarily for information professionals, using a command language interface. In addition to CAS databases, STN also provides access to other databases. SciFinder is a database of chemical and bibliographic information, originally a client application, a web version was released in 2008. It has an interface, and can be searched for chemical structures. The client version is for chemists in commercial organizations, versions for both the Windows and Macintosh exist. SciFinder Scholar is for universities and other institutions and lacks some supplementary features for multi-database searching. CASSI stands for Chemical Abstracts Service Source Index, since 2009 this formerly print and CD-ROM compilation is available as a free online resource to look up and confirm publication information. The online CASSI Search Tool provides titles and abbreviations, CODEN, ISSN, publisher, also included is its language of text and language of summaries. The range is from 1907 to the present, including serial and non-serial scientific and technical publications. Beyond CASSI lists abbreviated journal titles from early literature and other historical reference sources. Chemical Abstracts began as an effort and developed from there. The use of volunteer abstractors was phased out in 1994, Chemical Abstracts has been associated with the American Chemical Society in one way or another since 1907. For many years, beginning in 1909, the offices of Chemical Abstracts were housed in places on the campus of Ohio State University in Columbus
4.
International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
