I was looking up some ion channel blockers. What does (+) or (-) below mean?
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Bicuculline is a chiral molecule. That means that its mirror images are non-superimposable. These non-superimposable images are termed "enantiomers." When you see a "(+)" or "(-)" in front of a chemical name it tells you that only one the enantiomers is present (e.g. it is not a racemic mixture of the enantiomers). Chiral molecules have the ability to rotate the plane of a polarized light beam that passes through it. Enantiomers will rotate the plane of polarization in exactly equal amounts (same magnitude) but in opposite directions.
Dextrorotary designated as (+), indicates clockwise rotation (to the right)
Levorotary designated as (-), indicates anti-clockwise rotation (to the left)
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$\begingroup$ You should also mention that dextrorotary is designated as D (D-Glucose) and levorotary as L (L-tyrosine). But there are some exceptions. L-alanine and a few more L-amino acids are dextrorotary and some D-sugars are levorotary. $\endgroup$– LDC3Commented Jun 2, 2014 at 2:38
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$\begingroup$ @ron could you please comment why chemistry.mcmaster.ca/~chem2ob3/nhw_temp/old_old_labmanual/… page shows (R)-(-)-Carvone? Wouldn't R (to the right) match with a (+) ? $\endgroup$ Commented Dec 17, 2016 at 3:45
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2$\begingroup$ @K-Feldspar No, R and S are nomenclature terms that describe the spatial configuration at a chiral carbon using the Cahn-Ingold-Prelog priority system. (+) and (-) describe the direction of rotation of polarized light when it passes through the sample. There is no relationship between R and S and (+) and (-). $\endgroup$– ronCommented Dec 17, 2016 at 14:54