In chemistry, a glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate. A glycosidic bond is formed between the hemiacetal or hemiketal group of a saccharide and the hydroxyl group of some compound such as an alcohol. A substance containing a glycosidic bond is a glycoside; the term'glycoside' is now extended to cover compounds with bonds formed between hemiacetal groups of sugars and several chemical groups other than hydroxyls, such as -SR, -SeR, -NR1R2, or -CR1R2R3. In occurring glycosides, the compound ROH from which the carbohydrate residue has been removed is termed the aglycone, the carbohydrate residue itself is sometimes referred to as the'glycone'. Glycosidic bonds of the form discussed above are known as O-glycosidic bonds, in reference to the glycosidic oxygen that links the glycoside to the aglycone or reducing end sugar. In analogy, one considers S-glycosidic bonds, where the oxygen of the glycosidic bond is replaced with a sulfur atom.
In the same way, N-glycosidic bonds, have the glycosidic bond oxygen replaced with nitrogen. Substances containing N-glycosidic bonds are known as glycosylamines. C-glycosyl bonds have the glycosidic oxygen replaced by a carbon. All of these modified glycosidic bonds have different susceptibility to hydrolysis, in the case of C-glycosyl structures, they are more resistant to hydrolysis. One distinguishes between α- and β-glycosidic bonds based on the relative stereochemistry of the anomeric position and the stereocenter furthest from C1 in the saccharide. An α-glycosidic bond is formed when both carbons have the same stereochemistry, whereas a β-glycosidic bond occurs when the two carbons have different stereochemistry. One complicating issue is that the alpha and beta conformations were defined based on the relative orientation of the major constituents in a Haworth projection. In this case, for D-sugars, a beta conformation would see the major constituent at each carbon drawn above the plane of the ring, while alpha would see the anomeric constituent below the ring.
For L-sugars, the definitions would necessarily, reverse. This is worth noting as these older definitions still permeate the literature and can lead to confusion. Pharmacologists join substances to glucuronic acid via glycosidic bonds in order to increase their water solubility. Many other glycosides have important physiological functions. Nüchter et al. have shown a new approach to Fischer Glycosylation. Employing a microwave oven equipped with refluxing apparatus in a rotor reactor with pressure bombs, Nüchter et al. were able to achieve 100% yield of α- and β-D-glucosides. This method can be performed on a multi-kilogram scale. Vishal Y Joshi's method Joshi et al. propose the Koenigs-Knorr method in the stereoselective synthesis of alkyl D-glucopyranosides via glycosylation, with the exception of using lithium carbonate, less expensive and toxic than the conventional method of using silver or mercury salts. D-glucose is first protected by forming the peracetate by addition of acetic anhydride in acetic acid, addition of hydrogen bromide which brominates at the 5-position.
On addition of the alcohol ROH and lithium carbonate, the OR replaces the bromine and on deprotecting the acetylated hydroxyls the product is produced in high purity. It was suggested by Joshi et al. that lithium acts as the nucleophile that attacks the carbon at the 5-position and through a transition state the alcohol is substituted for the bromine group. Advantages of this method as well as its stereoselectivity and low cost of the lithium salt include that it can be done at room temperature and its yield compares well with the conventional Koenigs-Knorr method. Glycoside hydrolases, are enzymes. Glycoside hydrolases can act either on α- or on β-glycosidic bonds, but not on both; this specificity allows researchers to obtain glycosides in high epimeric excess, one example being Wen-Ya Lu's conversion of D-Glucose to Ethyl β-D-glucopyranoside using naturally-derived glucosidase. It is worth noting that Wen-Ya Lu utilized glucosidase in a reverse manner opposite to the enzyme's biological functionality: Before monosaccharide units are incorporated into glycoproteins, polysaccharides, or lipids in living organisms, they are first "activated" by being joined via a glycosidic bond to the phosphate group of a nucleotide such as uridine diphosphate, guanosine diphosphate, thymidine diphosphate, or cytidine monophosphate.
These activated biochemical intermediates are known as sugar nucleotides or sugar donors. Many biosynthetic pathways use mono- or oligosaccharides activated by a diphosphate linkage to lipids, such as dolichol; these activated donors are substrates for enzymes known as glycosyltransferases, which transfer the sugar unit from the activated donor to an accepting nucleophile. Different biocatalytic approaches has been developed toward the synthesis of glycosides in the past decades, which using “glycosyltransferases” and “glycoside hydrolases” are among the most common catalysis; the former needs expensive materials and the often shows low yields, De Winter et al. investigated use of cellobiose phosphorylase toward synthesis of alpha-glycosides in ionic liquids. The best condition f
X-ray crystallography is a technique used for determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their crystallographic disorder, various other information. Since many materials can form crystals—such as salts, minerals, semiconductors, as well as various inorganic and biological molecules—X-ray crystallography has been fundamental in the development of many scientific fields. In its first decades of use, this method determined the size of atoms, the lengths and types of chemical bonds, the atomic-scale differences among various materials minerals and alloys; the method revealed the structure and function of many biological molecules, including vitamins, drugs and nucleic acids such as DNA.
X-ray crystallography is still the primary method for characterizing the atomic structure of new materials and in discerning materials that appear similar by other experiments. X-ray crystal structures can account for unusual electronic or elastic properties of a material, shed light on chemical interactions and processes, or serve as the basis for designing pharmaceuticals against diseases. In a single-crystal X-ray diffraction measurement, a crystal is mounted on a goniometer; the goniometer is used to position the crystal at selected orientations. The crystal is illuminated with a finely focused monochromatic beam of X-rays, producing a diffraction pattern of spaced spots known as reflections; the two-dimensional images taken at different orientations are converted into a three-dimensional model of the density of electrons within the crystal using the mathematical method of Fourier transforms, combined with chemical data known for the sample. Poor resolution or errors may result if the crystals are too small, or not uniform enough in their internal makeup.
X-ray crystallography is related to several other methods for determining atomic structures. Similar diffraction patterns can be produced by scattering electrons or neutrons, which are interpreted by Fourier transformation. If single crystals of sufficient size cannot be obtained, various other X-ray methods can be applied to obtain less detailed information. If the material under investigation is only available in the form of nanocrystalline powders or suffers from poor crystallinity, the methods of electron crystallography can be applied for determining the atomic structure. For all above mentioned X-ray diffraction methods, the scattering is elastic. By contrast, inelastic X-ray scattering methods are useful in studying excitations of the sample such as plasmons, crystal-field and orbital excitations and phonons, rather than the distribution of its atoms. Crystals, though long admired for their regularity and symmetry, were not investigated scientifically until the 17th century. Johannes Kepler hypothesized in his work Strena seu de Nive Sexangula that the hexagonal symmetry of snowflake crystals was due to a regular packing of spherical water particles.
The Danish scientist Nicolas Steno pioneered experimental investigations of crystal symmetry. Steno showed that the angles between the faces are the same in every exemplar of a particular type of crystal, René Just Haüy discovered that every face of a crystal can be described by simple stacking patterns of blocks of the same shape and size. Hence, William Hallowes Miller in 1839 was able to give each face a unique label of three small integers, the Miller indices which remain in use today for identifying crystal faces. Haüy's study led to the correct idea that crystals are a regular three-dimensional array of atoms and molecules. In the 19th century, a complete catalog of the possible symmetries of a crystal was worked out by Johan Hessel, Auguste Bravais, Evgraf Fedorov, Arthur Schönflies and William Barlow. From the available data and physical reasoning, Barlow proposed several crystal structures in the 1880s that were validated by X-ray crystallography. Wilhelm Röntgen discovered X-rays in 1895, just as the studies of crystal symmetry were being concluded.
Physicists were uncertain of the nature of X-rays, but soon suspected that they were waves of electromagnetic radiation—in other words, another form of light. At that time, the wave model of light—specifically, the Maxwell theory of electromagnetic radiation—was well accepted among scientists, experiments by Charles Glover Barkla showed that X-rays exhibited phenomena associated with electromagnetic waves, including transverse polarization and spectral lines akin to those observed in the visible wavelengths. Single-slit experiments in the laboratory of Arnold Sommerfeld suggested that X-rays had a wavelength of about 1 angstrom. However, X-rays are composed of photons, thus are not only waves of electromagnetic radiation but exhibit particle-like properties. Albert Einstein introduced the photon concept in 1905, but it was not broadly accepted until 1922, when Arthur
A glucuronide known as glucuronoside, is any substance produced by linking glucuronic acid to another substance via a glycosidic bond. The glucuronides belong to the glycosides. Glucuronidation, the conversion of chemical compounds to glucuronides, is a method that animals use to assist in the excretion of toxic substances, drugs or other substances that cannot be used as an energy source. Glucuronic acid is attached via a glycosidic bond to the substance, the resulting glucuronide, which has a much higher water solubility than the original substance, is excreted by the kidneys. Enzymes that cleave the glycosidic bond of a glucuronide are called glucuronidases. Miquelianin Morphine-6-glucuronide Scutellarein-7-glucuronide
The Jmol applet, among other abilities, offers an alternative to the Chime plug-in, no longer under active development. While Jmol has many features that Chime lacks, it does not claim to reproduce all Chime functions, most notably, the Sculpt mode. Chime requires plug-in installation and Internet Explorer 6.0 or Firefox 2.0 on Microsoft Windows, or Netscape Communicator 4.8 on Mac OS 9. Jmol operates on a wide variety of platforms. For example, Jmol is functional in Mozilla Firefox, Internet Explorer, Google Chrome, Safari. Chemistry Development Kit Comparison of software for molecular mechanics modeling Jmol extension for MediaWiki List of molecular graphics systems Molecular graphics Molecule editor Proteopedia PyMOL SAMSON Official website Wiki with listings of websites and moodles Willighagen, Egon. "Fast and Scriptable Molecular Graphics in Web Browsers without Java3D". Doi:10.1038/npre.2007.50.1
The Brussels sprout is a member of the Gemmifera Group of cabbages, grown for its edible buds. The leafy green vegetables are 1.5–4.0 cm in diameter and look like miniature cabbages. The Brussels sprout has long been popular in Brussels and may have gained its name there. Although native to the Mediterranean region with other cabbage species, Brussels sprouts first appeared in northern Europe during the fifth century being cultivated in the 13th century near Brussels, from which they derived their name, they may be called brussels sprouts, Brussel sprouts, or brussel sprouts. Forerunners to modern Brussels sprouts were cultivated in Ancient Rome. Brussels sprouts as they are now known were grown as early as the 13th century in what is now Belgium; the first written reference dates to 1587. During the 16th century, they enjoyed a popularity in the southern Netherlands that spread throughout the cooler parts of Northern Europe. Brussels sprouts grow in temperature ranges of 7–24 °C, with highest yields at 15–18 °C.
Fields are ready for harvest 90 to 180 days after planting. The edible sprouts grow like buds in helical patterns along the side of long, thick stalks of about 60 to 120 cm in height, maturing over several weeks from the lower to the upper part of the stalk. Sprouts may be picked by hand into baskets, in which case several harvests are made of five to 15 sprouts at a time, or by cutting the entire stalk at once for processing, or by mechanical harvester, depending on variety; each stalk can produce 1.1 to 1.4 kg. Harvest season in temperate zones of the northern latitudes is September to March, making Brussels sprouts a traditional winter-stock vegetable. In the home garden, harvest can be delayed. Sprouts are considered to be sweetest after a frost. Brussels sprouts are a cultivar group of the same species as broccoli, collard greens and kohlrabi. Many cultivars are available; the purple varieties are hybrids between purple cabbage and regular green Brussels sprouts developed by a Dutch botanist in the 1940s, yielding a variety with some of the red cabbage's purple colors and greater sweetness.
In Continental Europe, the largest producers are the Netherlands, at 82,000 metric tons, Germany, at 10,000 tons. The United Kingdom has production comparable to that of the Netherlands, but its crop is not exported. Production of Brussels sprouts in the United States began in the 18th century, when French settlers brought them to Louisiana; the first plantings in California's Central Coast began in the 1920s, with significant production beginning in the 1940s. Several thousand acres are planted in coastal areas of San Mateo, Santa Cruz, Monterey counties of California, which offer an ideal combination of coastal fog and cool temperatures year-round; the harvest season lasts from June through January. Most U. S. production is in California, with a smaller percentage of the crop grown in Skagit Valley, where cool springs, mild summers, rich soil abounds, to a lesser degree on Long Island, New York. Total U. S. production is with a value of $27 million. About 80 to 85% of U. S. production is with the remainder for fresh consumption.
Once harvested, sprouts last 3-5 weeks under ideal near-freezing conditions before wilting and discoloring, about half as long at refrigerator temperature. U. S. varieties are 2.5–5 cm in diameter. Raw Brussels sprouts are 86% water, 9% carbohydrates, 3% protein, contain negligible fat. In a 100 gram reference amount, they supply high levels of vitamin C and vitamin K, with more moderate amounts of B vitamins, such as folate and vitamin B6. Brussels sprouts, as with broccoli and other brassicas, contain sulforaphane, a phytochemical under basic research for its potential biological properties. Although boiling reduces the level of sulforaphane, neither steaming, microwave cooking, nor stir frying cause a significant loss. Consuming Brussels sprouts in excess may not be suitable for people taking anticoagulants, such as warfarin, since they contain vitamin K, a blood-clotting factor. In one incident, eating too many Brussels sprouts led to hospitalization for an individual on blood-thinning therapy.
The most common method of preparing Brussels sprouts for cooking begins with cutting the buds off the stalk. Any surplus stem is cut away, any loose surface leaves are peeled and discarded. Once cut and cleaned, the buds are cooked by boiling, stir frying, slow cooking, or roasting. To ensure cooking throughout, buds of a similar size are chosen; some cooks make a cross in the center of the stem to aid the penetration of heat. Overcooking renders the buds gray and soft, they develop a strong flavor and odor that some dislike for its garlic- or onion-odor properties; the odor is associated with the glucosinolate sinigrin, a sulfur compound having characteristic pungency. For taste, roasting Brussels sprouts is a common way to cook them to enhance flavor. Common toppings or additions for Brussels sprouts include Parmesan cheese and butter, balsamic vinegar, brown sugar, chestnuts, or pepper. Another way of cooking Brussels sprouts is to sauté them. Brussels sprouts can be pickled as an alternative to cooking
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
Saponins are a class of chemical compounds found in particular abundance in various plant species. More they are amphipathic glycosides grouped phenomenologically by the soap-like foam they produce when shaken in aqueous solutions, structurally by having one or more hydrophilic glycoside moieties combined with a lipophilic triterpene or steroid derivative; the aglycone portions of the saponins are termed sapogenins. The number of saccharide chains attached to the sapogenin/aglycone core can vary – giving rise to another dimension of nomenclature – as can the length of each chain. A somewhat dated compilation has the range of saccharide chain lengths being 1–11, with the numbers 2–5 being the most frequent, with both linear and branched chain saccharides being represented. Dietary monosaccharides such as D-glucose and D-galactose are among the most common components of the attached chains; the lipophilic aglycone can be any one of a wide variety of polycyclic organic structures originating from the serial addition of 10-carbon terpene units to compose a C30 triterpene skeleton with subsequent alteration to produce a C27 steroidal skeleton.
The subset of saponins that are steroidal have been termed saraponins. Aglycone derivatives can incorporate nitrogen, so some saponins present chemical and pharmacologic characteristics of alkaloid natural products; the figure at right above presents the structure of the alkaloid phytotoxin solanine, a monodesmosidic, branched-saccharide steroidal saponin. Saponins have been understood to be plant-derived, but they have been isolated from marine organisms such as sea cucumber. Saponins are indeed found in many plants, derive their name from the soapwort plant, the root of, used as a soap. Saponins are found in the botanical family Sapindaceae, with its defining genus Sapindus, in the related families Aceraceae and Hippocastanaceae, it is found in Gynostemma pentaphyllum in a form called gypenosides, ginseng or red ginseng in a form called ginsenosides. Saponins are found in the unripe fruit of Manilkara zapota, resulting in astringent properties. Within these families, this class of chemical compounds is found in various parts of the plant: leaves, roots, bulbs and fruit.
Commercial formulations of plant-derived saponins, e.g. from the soap bark tree, Quillaja saponaria, those from other sources are available via controlled manufacturing processes, which make them of use as chemical and biomedical reagents. Froth Test Uses plant Gogo Entada phaseoloides as control; the positive result shows a honeycomb froth, higher than 2 cm that persists for 10 minutes or longer. Blood Agar Media: Is an agar cup semi-quantitative method that shows positive result of hemolytic halos. In plants, saponins may serve as anti-feedants, to protect the plant against microbes and fungi; some plant saponins may enhance nutrient aid in animal digestion. However, saponins are bitter to taste, so can reduce plant palatability, or imbue them with life-threatening animal toxicity; some saponins are toxic to cold-blooded insects at particular concentrations. Further research is needed to define the roles of these natural products in their host organisms, which have been described as "poorly understood" to date.
Most saponins, which dissolve in water, are poisonous to fish. Therefore, in ethnobotany, they are known for their use by indigenous people in obtaining aquatic food sources. Since prehistoric times, cultures throughout the world have used piscicidal plants those containing saponins, for fishing. Although prohibited by law, fish poison plants are still used by indigenous tribes in Guyana. On the Indian Subcontinent, the Gond tribes are known for their use of plant extracts in poison fishing. Many of California's Native American tribes traditionally used soaproot, and/or the root of various yucca species, which contain saponin, as a fish poison, they would pulverize the roots, mixing in water to create a foam, add the suds to a stream. This would kill or incapacitate the fish, which could be gathered from the surface of the water. Among the tribes using this technique were the Lassik, the Luiseño, the Mattole; the amphipathic nature of saponins gives them activity as surfactants with potential ability to interact with cell membrane components, such as cholesterol and phospholipids making saponins useful for development of cosmetics and drugs.
Saponins have been used as adjuvants in development of vaccines, such as Quil A, an extract from the bark of Quillaja saponaria Molina. This makes them of interest for possible use in subunit vaccines and vaccines directed against intracellular pathogens. In their use as adjuvants in the production of vaccines, toxicity associated with sterol complexation remains a concern. While saponins are promoted commercially as dietary supplements and food ingredients, are used in traditional medicine preparations from licorice, there is no high-quality clinical evidence that they have any beneficial effect on human health. Quillaja is toxic when consumed in large