Chirality (chemistry)

In chemistry, a molecule or ion is called chiral if it cannot be superposed on its mirror image by any combination of rotations and translations. This geometric property is called chirality; the terms are derived from Ancient Greek χείρ, meaning "hand". A chiral molecule or ion exists in two stereoisomers that are mirror images of each other, called enantiomers; the two enantiomers have the same chemical properties, except when reacting with other chiral compounds. They have the same physical properties, except that they have opposite optical activities. A homogeneous mixture of the two enantiomers in equal parts is said to be racemic, it differs chemically and physically from the pure enantiomers. A chiral molecule or ion must have stereocenter; when that center coincides with an atom, the substance is said to have point chirality. In chiral organic compounds, a stereocenter is an asymmetric carbon. Multiple stereocenters may give rise to additional stereoisomers. On the other hand, a molecule with an number of stereocenters may have one or more stereoisomers which are not chiral.

Chirality is an important concept for biochemistry. Most substances relevant to biology are chiral, such as carbohydrates, the amino acids that are the building blocks of proteins, the nucleic acids. In living organisms, one finds only one of the two enantiomers or a chiral compound. For that reason, organisms that consume a chiral compound can metabolize only one of its enantiomers. For the same reason, the two enantiomers of a chiral pharmaceutical have vastly different potencies and/or effects. Chirality is based on molecular symmetry. A chiral compound can contain no improper axis of rotation, which includes planes of symmetry and inversion center. Chiral molecules are always dissymmetric but not always asymmetric. Asymmetric molecules are always chiral. Many chiral molecules have point chirality, namely a single stereogenic center that coincides with an atom; this stereogenic center has four or more bonds to different groups, may be carbon, silicon, or a metal. However, a stereogenic center can be a trivalent atom whose bonds are not in the same plane, such as phosphorus in P-chiral phosphines and sulfur in S-chiral sulfoxides.

Chirality can arise from isotopic differences between atoms, such as in the deuterated benzyl alcohol PhCHDOH. If two enantiomers interconvert, the pure enantiomers may be impossible to separate, only the racemic mixture is observable; this is the case, for example, of most amines with three different substituents, because of the low energy barrier for nitrogen inversion. While the presence of a stereogenic center describes the great majority of chiral molecules, many variations and exceptions exist. For instance it is not necessary for the chiral substance to have a stereogenic center. Examples include 1-bromo-3-chloro-5-fluoroadamantane, methylethylphenyltetrahedrane, certain calixarenes and fullerenes, which have inherent chirality; the C2-symmetric species 1,1′-bi-2-naphthol, 1,3-dichloroallene have axial chirality. -cyclooctene and many ferrocenes have planar chirality. When the optical rotation for an enantiomer is too low for practical measurement, the species is said to exhibit cryptochirality.

Flavour: the artificial sweetener aspartame has two enantiomers. L-aspartame tastes sweet. Odor: R--carvone smells like spearmint whereas S--carvone smells like caraway. Drug effectiveness: the antidepressant drug Citalopram is sold as a racemic mixture. However, studies have shown that only the - enantiomer is responsible for the drug's beneficial effects. Drug safety: D‑penicillamine is used in chelation therapy and for the treatment of rheumatoid arthritis whereas L‑penicillamine is toxic as it inhibits the action of pyridoxine, an essential B vitamin. Many biologically active molecules are chiral, including the occurring amino acids and sugars; the origin of this homochirality in biology is the subject of much debate. Most scientists believe that Earth life's "choice" of chirality was purely random, that if carbon-based life forms exist elsewhere in the universe, their chemistry could theoretically have opposite chirality. However, there is some suggestion. In this case, circularly polarised radiation could have caused the selective destruction of one chirality of amino acids, leading to a selection bias which resulted in all life on Earth being homochiral.

Enzymes, which are chiral distinguish between the two enantiomers of a chiral substrate. One could imagine an enzyme as having a glove-like cavity. If this glove is right-handed one enantiomer will fit inside and be bound, whereas the other enantiomer will have a poor fit and is unlikely to bind. L-forms of amino acids tend to be tasteless. Spearmint leaves contain the L-enantiomer of the chemical carvone or R--carvone and caraway seeds contain the D-enantiomer or S--carvone; the two smell different to most people because our olfactory recept

Stuyvesant Handicap

The Stuyvesant Handicap is an American thoroughbred horse race held in the fall of the year at Aqueduct Race Track in Queens, New York. A Grade III event, it is set over nine furlongs on the dirt for three-year-olds and up; the Stuyvesant, named for an area of New York City settled by the Dutch in the dawn of what would become America, offers a purse of $100,000 added. The Stuyvesant was run at Jamaica for only three-year-olds from 1916 to 1924, from 1937 to 1939. In 1916, 1917, 1918, again from 1937 to 1939 it was a six furlong sprint, it went off at a mile from 1919 to 1924 and from 1964 to 1972. It was not run at all from 1925 to 1936, nor from 1940 to 1962, it took place at Belmont Park in 1990, 1995, 2001. It has been run at Aqueduct all other years since 1963; the 1978 running was the swan song for the 1977 Triple Crown winner. Slew, ridden by Angel Cordero, Jr. winning the race by four lengths. Sportscaster and Aqueduct track announcer Chic Anderson called the race's climax movingly: "Ladies and gentlemen, here he is, the champion of the world, Seattle Slew!"

The Stuyvesant would have been in its 59th running in 2009, but was canceled because of lack of interest. Five starters were entered. Two inches of rain was predicted for the day of the Stuyvesant. 2008 - Dry Martini 2007 - Hunting - 2006 - Accountforthegold 2005 - Evening Attire 2004 - Classic Endeavor 2003 - Presidentialaffair 2002 - Snake Mountain 2001 - Graeme Hall 2000 - Lager 1999 - Best of Luck 1998 - Mr. Sinatra 1997 - Delay of Game 1996 - Poor But Honest 1995 - Silver Fox 1994 - Wallenda 1993 - Michelle Can Pass 1992 - Shots Are Ringing 1991 - Montubio 1990 - Im Sky High 1989 - Its Academic 1988 - Talinum 1987 - Moment Of Hope 1986 - Little Missouri 1985 - Garthorn 1984 - Valiant Lark 1983 - Fit to Fight 1982 - Engine One 1981 - Idyll 1980 - Plugged Nickle 1979 - Music of Time 1978 - Seattle Slew 1977 - Cox's Ridge 1976 - Distant Land 1975 - Festive Mood 1974 - Crafty Khale 1973 - Riva Ridge 1972 - Icecapade 1971 - Red Reality 1970 - Never Bow 1969 - King Emperor 1968 - Spring Double 1967 - Sun Gala 1966 - Understanding 1965 - Flag Raiser 1964 - Macedonia 1963 - Rocky Link 1939 - T. M. Dorsett 1938 - Merry Lassie 1937 - Chicolorado 1924 - Ordinance 1923 - Dot 1922 - Snob II 1921 - Sedgefield 1920 - Man o' War 1919 - Purchase 1918 - Motor Cop 1917 - Julialeon 1916 - Fernrock

Bryan Orritt

Bryan Orritt was a Welsh professional footballer who played as an inside forward or wing half. He made more than 200 appearances in the Football League, was capped three times for Wales at under-23 level. Born in Caernarfon, Orritt began his football career with local club Llanfair PG before joining Bangor City. In 1956 he joined English First Division club Birmingham City, for whom he went on to play in the finals of the 1960 and 1961 Inter-Cities Fairs Cups, becoming one of the first Welsh footballers to take part in European competition. In 1962 he moved to Middlesbrough, became the first substitute used by the club, he emigrated to South Africa, playing for and managing Southern Suburbs F. C. Orritt died in a Johannesburg nursing home on 24 March 2014 at the age of 77. GeneralMatthews, Tony. Birmingham City: A Complete Record. Derby: Breedon Books. ISBN 1-85983-010-2. Specific Profile at The Citizens Choice, a Bangor City unofficial site