International Standard Serial Number
An International Standard Serial Number is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine. The ISSN is helpful in distinguishing between serials with the same title. ISSN are used in ordering, interlibrary loans, other practices in connection with serial literature; the ISSN system was first drafted as an International Organization for Standardization international standard in 1971 and published as ISO 3297 in 1975. ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard; when a serial with the same content is published in more than one media type, a different ISSN is assigned to each media type. For example, many serials are published both in electronic media; the ISSN system refers to these types as electronic ISSN, respectively. Conversely, as defined in ISO 3297:2007, every serial in the ISSN system is assigned a linking ISSN the same as the ISSN assigned to the serial in its first published medium, which links together all ISSNs assigned to the serial in every medium.
The format of the ISSN is an eight digit code, divided by a hyphen into two four-digit numbers. As an integer number, it can be represented by the first seven digits; the last code digit, which may be 0-9 or an X, is a check digit. Formally, the general form of the ISSN code can be expressed as follows: NNNN-NNNC where N is in the set, a digit character, C is in; the ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, C=5. To calculate the check digit, the following algorithm may be used: Calculate the sum of the first seven digits of the ISSN multiplied by its position in the number, counting from the right—that is, 8, 7, 6, 5, 4, 3, 2, respectively: 0 ⋅ 8 + 3 ⋅ 7 + 7 ⋅ 6 + 8 ⋅ 5 + 5 ⋅ 4 + 9 ⋅ 3 + 5 ⋅ 2 = 0 + 21 + 42 + 40 + 20 + 27 + 10 = 160 The modulus 11 of this sum is calculated. For calculations, an upper case X in the check digit position indicates a check digit of 10. To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right.
The modulus 11 of the sum must be 0. There is an online ISSN checker. ISSN codes are assigned by a network of ISSN National Centres located at national libraries and coordinated by the ISSN International Centre based in Paris; the International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government. The International Centre maintains a database of all ISSNs assigned worldwide, the ISDS Register otherwise known as the ISSN Register. At the end of 2016, the ISSN Register contained records for 1,943,572 items. ISSN and ISBN codes are similar in concept. An ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change. Since the ISSN applies to an entire serial a new identifier, the Serial Item and Contribution Identifier, was built on top of it to allow references to specific volumes, articles, or other identifiable components.
Separate ISSNs are needed for serials in different media. Thus, the print and electronic media versions of a serial need separate ISSNs. A CD-ROM version and a web version of a serial require different ISSNs since two different media are involved. However, the same ISSN can be used for different file formats of the same online serial; this "media-oriented identification" of serials made sense in the 1970s. In the 1990s and onward, with personal computers, better screens, the Web, it makes sense to consider only content, independent of media; this "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred. A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application. An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier, as ISSN-independent initiative, consolidated in the 2000s. Only in 2007, ISSN-L was defined in the
Cyclodextrins are a family of cyclic oligosaccharides, consisting of a macrocyclic ring of glucose subunits joined by α-1,4 glycosidic bonds. Cyclodextrins are produced from starch by enzymatic conversion, they are used in food, drug delivery, chemical industries, as well as agriculture and environmental engineering. Cyclodextrins are composed of 5 or more α-D-glucopyranoside units linked 1->4, as in amylose. The largest cyclodextrin contains 32 1,4-anhydroglucopyranoside units, while as a poorly characterized mixture, at least 150-membered cyclic oligosaccharides are known. Typical cyclodextrins contain a number of glucose monomers ranging from six to eight units in a ring, creating a cone shape: α -cyclodextrin: 6 glucose subunits β -cyclodextrin: 7 glucose subunits γ -cyclodextrin: 8 glucose subunits With an hydrophobic interior and hydrophilic exterior, cyclodextrins form complexes with hydrophobic compounds. Alpha-, beta-, gamma-cyclodextrin are all recognized as safe by the U. S. FDA, they have been applied for delivery of a variety of drugs, including hydrocortisone, nitroglycerin, chloramphenicol.
The cyclodextrin confers stability to these drugs. The inclusion compounds of cyclodextrins with hydrophobic molecules are able to penetrate body tissues, these can be used to release biologically active compounds under specific conditions. In most cases the mechanism of controlled degradation of such complexes is based on pH change of water solutions, leading to the loss of hydrogen or ionic bonds between the host and the guest molecules. Alternative means for the disruption of the complexes take advantage of heating or action of enzymes able to cleave α-1,4 linkages between glucose monomers. Cyclodextrins were shown to enhance mucosal penetration of drugs. Β-cyclodextrins are used to produce stationary phase media for HPLC separations. Cyclodextrins bind fragrances; such devices are capable of releasing fragrances during ironing or when heated by human body. They are the main ingredient in Febreze which claims that the β-cyclodextrins "trap" odor causing compounds, thereby reducing the odor.
Such a device used is a typical'dryer sheet'. The heat from a clothes dryer releases the fragrance into the clothing. Cyclodextrins are used to produce alcohol powder by encapsulating ethanol; the powder produces an alcoholic beverage when mixed with water. Typical cyclodextrins are constituted by 6-8 glucopyranoside units; these subunits are linked by 1,4 glycosidic bonds. The cyclodextrins have toroidal shapes, with the larger and the smaller openings of the toroid exposing to the solvent secondary and primary hydroxyl groups respectively; because of this arrangement, the interior of the toroids is not hydrophobic, but less hydrophilic than the aqueous environment and thus able to host other hydrophobic molecules. In contrast, the exterior is sufficiently hydrophilic to impart cyclodextrins water solubility, they are not soluble in typical organic solvents. Cyclodextrins are prepared by enzymatic treatment of starch. Cyclodextrin glycosyltransferase is employed along with α-amylase. First starch is liquified either by heat treatment or using α-amylase CGTase is added for the enzymatic conversion.
CGTases produce mixtures of cyclodextrins, thus the product of the conversion results in a mixture of the three main types of cyclic molecules, in ratios that are dependent on the enzyme used: each CGTase has its own characteristic α:β:γ synthesis ratio. Purification of the three types of cyclodextrins takes advantage of the different water solubility of the molecules: β-CD, poorly water-soluble can be retrieved through crystallization while the more soluble α- and γ-CDs are purified by means of expensive and time consuming chromatography techniques; as an alternative a "complexing agent" can be added during the enzymatic conversion step: such agents form a complex with the desired cyclodextrin which subsequently precipitates. The complex formation drives the conversion of starch towards the synthesis of the precipitated cyclodextrin, thus enriching its content in the final mixture of products. Wacker Chemie AG uses dedicated enzymes, that can produce alpha-, beta- or gamma-cyclodextrin specifically.
This is valuable for the food industry, as only alpha- and gamma-cyclodextrin can be consumed without a daily intake limit. Interest in cyclodextrins is enhanced because their host–guest behavior can be manipulated by chemical modification of the hydroxyl groups. O-Methylation and acetylation are typical conversions. Propylene oxide gives hydroxypropylated derivatives; the primary alcohols can be tosylated. The degree of derivatization is an i.e. full methylation vs partial. Both β-cyclodextrin and methyl-β-cyclodextrin remove cholesterol from cultured cells; the methylated form MβCD was found to be more efficient than β-cyclodextrin. The water-soluble MβCD is known to form soluble inclusion complexes with cholesterol, thereby enhancing its solubility in aqueous solution. MβCD is employed for the preparation of cholesterol-free products: the bulky and hydrophobic cholesterol molecule is lodged inside cyclodextrin rings. MβCD is employed in research to disrupt lipid rafts by removing cholesterol from membranes.
In supramolecular chemistry, cyclodextrins are precursors to mechanically interlocked molecular architectures, such as rotaxanes and catenanes. Illustrative, α-cyclodextrin form second-sphere coordination complex with tetrabromoaurate anion. Beta-cyclodextrin complexes with certain c