what is enantiometric enrichment?
344456
An enantiomeric ratio (ER) is defined as the (+)-enantiomer concentration of a chiral compound divided by its (-)-enantiomer concentration (Vetter and Schurig 1997):\n\n\n                      ER = (+)-enantiomer / (-)-enantiomer                                     (1) \n\nThe (+)-sign indicates that the enantiomer rotates a plane of polarized light to the right (clockwise; March 1985). The isomer with the (-)-sign rotates the light to the left (counterclockwise). Chiroptical detection is not always included in chiral chromatographic analysis. Also, pure enantiomers or enantiomeric enriched reference materials may not be available; therefore the enantiomer elution sequence cannot be achieved. In such cases, the ER is defined as the concentration of the first eluting enantiomer divided by the second enantiomer, under precisely defined chromatographic conditions (Vetter and Schurig 1997). Nowadays, pure enantiomer or enantiomer enriched standards are often available and the elution sequence can be easily determined (Müller and Buser 1994). \n\n\n\nMany organic compounds contain multiple chiral centres.  These are all essentially the same compound, but exist as mirror images of each other (compare with your left and right hand - they are the same, only your left hand can do different things to your right).  Many durgs contain chiral centres, and often several, and it is necessary to ensure there is a process to prepare a specific mirror image.  Giving a patient the "wrong" enantiomer can have serious side effects, or be completely inactive. (Thalidomide being a famous example)\n\nWhere a compound has two or more chrial centres then enantiomers exist.  For example the (R,R) isomer of one molecule is the opposite enantiomer to the (S,S) isomer of the same.  The structure of each look identical, but they are in fact mirror images.  It is not possible to superimpose one on the other.  Enantiomeric enrichment is where a process is introduced to selectively extract one enantiomer from the other, and therefore increase the amount of one compound over the other.  There are many ways to do this, however a common way is to complex selectively the required isomer with another chiral compound, and crytallise this complex from solution.  \n\nExamples escape me I'm afraid, but I'll try.  If you have 100 blue smarties and 100 red smarties.  These are the same, with the exception of colour (replace this with mirror image in chirality and you might see a tentative link...?).  This is a 50:50 mix.  If you introduce your baby sister to these smarties, and she prefers the blue ones, then she'll eat all of those, leaving the red ones behind.  What you have left therefore is an enriched quantity of red smarties.  If all goes well, then you will have 100% red smarties.  What you have done is enriched your mix.  Enantiomeric enrichment is the same principle.  Keeping what you want, but throwing away what you don't.\n\nAlternatively you can isomerise the undesired enantiomer into the desired enantiomer by chemical means.  This depends upon the relative energy states of each enantiomer and which one is the preferred form.  Either way the amount of desired product you have formed increases and you have enriched your mixture.\n\nI am not sure if any of this makes sense, as it is very difficult to explain without pictures.\n\nI've ahd a look and added a couple of links which may help.
427158
Actually they are not. As a previous answerer already pointed out, many molecules are exist in left-handed and right-handed variety. \n\nBut I suppose the question you are interested is why in biological systems most of these compounds are of the same chirality? \n\nNaturally biologically-active molecules are often chiral, including amino acids (the building blocks of proteins), and sugars. Most amino acids are L and sugars are D. The origin of this homochirality in biology is the subject of debate. As the two systems would work, there is no particular reason that L amino acids and D sugars are prefered in nature. However, the two systems don't mix. Therefore the usual reason given is that early on in life's history one system was slightly more abundant than the other. Once this imbalance existed it can only become larger. The more abondant system takes more of the available resources and quickly crowds out the other one.
306417
Circular dichroism (CD), is the differential absorption of left- and right-handed circularly polarized light. It is a form of spectroscopy used to determine the optical isomerism and secondary structure of molecules.\n\nAt a given wavelength,\n\nΔA = (AL − AR) \nwhere ΔA is the difference between absorbance of left circularly polarized (LCP) and right circularly polarized (RCP) light (this is what is usually measured). It can also be expressed as:\n\nΔA = (εL − εR) C l \nwhere εL and εR are the molar extinction coefficients for RCP and LCP light, where C is the molar concentration and l is path length.\n\nThen\n\nΔε = (εL − εR) \nis the molar circular dichroism. This is what is usually meant by the circular dichroism of the substance.\n\nAlthough ΔA is usually measured, for historical reasons most measurements are reported in degrees of ellipticity.\n\nThe molar ellipticity is:\n\n[θ] = 3298Δε. \nIn general, this phenomenon will be exhibited in absorption bands of any optically active molecule. As a consequence, circular dichroism is exhibited by biological molecules, because of the dextrorotary (e.g. some sugars) and levorotary (e.g. some amino acids) molecules they contain. Noteworthy as well is that secondary structure will also impart a distinct CD to their respective molecules. Therefore, the alpha helix of proteins and the double helix of nucleic acids have CD spectral signatures representative of their structures.\n\nCD is closely related to the optical rotary dispersion (ORD) technique, and is generally considered to be more advanced. CD is measured in or near the absorption bands of the molecule of interest, while ORD can be measured far from these bands. In principle these two spectral measurements can be interconverted through an integral transform, if all the absorptions are included in the measurements.\n\nThe ultraviolet CD spectrum of proteins can predict important characteristics of their secondary structure. CD spectra can be readily used to estimate the fraction of a molecule that is in the alpha-helix conformation, the beta-sheet conformation, the beta-turn conformation, or some other (random) conformation. These fractional assignments place important constraints on the possible secondary conformations that the protein can be in. CD cannot, in general, say where the alpha helices that are detected are located within the molecule or even completely predict how many there are. Despite this, CD is a valuable tool, especially for showing changes in conformation. It can, for instance, be used to study how the secondary structure of a molecule changes as a function of temperature or of the concentration of denaturing agents. In this way it can reveal important thermodynamic information about the molecule that cannot otherwise be easily obtained. Anyone attempting to study a protein will find CD a valuable tool for verifying that the protein is in its native conformation before undertaking extensive and/or expensive experiments with it. Also, there are a number of other uses for CD spectroscopy in protein chemistry not related to alpha-helix fraction estimation. s\n\nCD spectroscopy is usually used to study proteins in solution, and thus it complements methods that study the solid state. This is also a limitation, in that many proteins are embedded in membranes in their native state, and solutions containing membrane structures are often strongly scattering. CD is sometimes measured in thin films.\nCD has also been studied in carbohydrates, but with limited success due to the experimental difficulties associated with measurement of CD spectra in the vacuum ultraviolet (VUV) region of the spectrum (100-200 nm), where the corresponding CD bands of unsubstituted carbohydrates lie. Substituted carbohydrates with bands above the VUV region have been successfully measured.\n\nMeasurement of CD is also complicated by the fact that typical aqueous buffer systems often absorb in the range where structur
823978
there is only one chiral center.  steriogenic centers are when there are 4 different groups on the same C.
492829
Hmm, the alpha-hydroxy carbon (CHOH) in benzoin is chiral:\n\nC6H6-CHOH-C(O)-C6H6\n\nso there should be optical activity.  These journal articles indicate that benzoin is optically active:\n\nhttp://turmac13.chem.columbia.edu/PDF_db/publications_401_450/444.pdf\nhttp://www.garfield.library.upenn.edu/histcomp/born-m_auth-citing/index-tc-99.html#\n\nPerhaps, if you are measuring a sample of benzoin made in the lab, you have a racemic mixture of enantiomers.  That would explain a lack of measurable optical activity.
721022
Well, I do not know that syllabus.  You will need to sift useful answers.\n\nI would use:\n\ndifferent solubility in solvents\ndifferent boiling points\nrecrystallise one out of a mixed solution\n\nYou might be at too junior a level to know about ion exchange resins, and other chromatography techniques.
978661
Have fun:\nhttp://www.math.nyu.edu/~griffith/teaching/06numanalysis/labs/bisection/
794130
Do you mean enrichment?\n\nIf so \n\nNE is the process of concentrating specific isotopes of a chemical element by removing other isotopes, for example separating natural uranium into enriched uranium and depleted uranium. This is the crucial process in the creation of a nuclear weapon.\n\nWhile in general chemical elements can be purified through chemical processes, isotopes of the same element have nearly identical chemical properties, which makes this type of separation impractical, except for separation of deuterium.
800470
That depends on your research study. Use NMR to obtain physical, chemical, electronic and structural information about a molecule. This is the only technique that can provide detailed information on the exact three-dimensional structure of biological molecules in solution. \n\nMass spectrometry on the other hand,  is used to measure the mass-to-charge ratio of ions. It is most generally used to find the composition of a physical sample by generating a mass spectrum representing the masses of sample components. It can also be used in these applications:\n\n-identifying unknown compounds by the mass of the compound molecules or their fragments \n-determining the isotopic composition of elements in a compound \n-determining the structure of a compound by observing its fragmentation \n-quantifying the amount of a compound in a sample using carefully designed methods (mass spectrometry is not inherently quantitative) \n-studying the fundamentals of gas phase ion chemistry (the chemistry of ions and neutrals in vacuum) \n-determining other physical, chemical or even biological properties of compounds with a variety of other approaches
610526
No.  Ibuprofen, like other 2-arylpropionate derivatives (including ketoprofen, flurbiprofen, naproxen, etc) contains a chiral carbon in the α-position of the propionate moiety. As such there are two possible enantiomers of ibuprofen with the potential for different biological effects and metabolism for each enantiomer.
864593
The difference is simple, an asymmetric carbon is simply a carbon surrounded by 4 different functional groups or atoms.\n\nTo understand the concept of dissymetric carbon we have tp explore the concept of sterioisomerism-OPTICAL ISOMERISM.\nA dissymetric carbon compound is such whose mirror image is not superimposible on it , in the language of organic chemistry, it \nexhibits CHIRALITY and OPTICAL ISOMERISM.\n\nI HOPE THIS WILL HELP U. IF U WAN'T MORE HELP, THEN U MAY REFER TO ANY GOOD BOOK ON ORGANIC CHEMISTRY, IN IT U CAN CONSULT FROM THE CHAPTER ISOMERISM.
215412
That is an IUPAC name, although it is an unspecified stereochemistry (the 2 and 3 positions can each be either R or S).\n\nThe trivial name for hexanoic acid is caproic acid.
1113616
I din't find that word in any dictionary.  The closest suggestion is enantiomorph.
1152693
enantiomeric excess (%) = \n(specific rotation of the mixture/ specific rotation of the pure enantiomer in excess)*100 \n\nor \n\nenantiomeric excess (%) = \n( | [enantiomer 1] - [enantiomer 1] | ) /([enantiomer 1] + [enantiomer 1] *100 \n\nwhere the square brackets indicate concentrations, and the | -- | in the numerator means "absolute value".
460267
A mono Q column is loaded with very small beads that seperate molecules, usually proteins, by anion exchange- im not sure what level of detail you want.
279023
Actually called: "Total nutrient admixture(TNA), A 3-in-1, or an all-in-one solution containing,:Dextrose, amino acids, and lipids. A 2-in-1 excludes lipids. There is no "name-brand" I know. They're looking for: "TNA", believe me!
809710
is you mean mass spectroscopy.. try this link...