I was looking up some ion channel blockers. What does (+) or (-) below mean?


(-)-Bicuculline methiodide

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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. $\endgroup$ – LDC3 Jun 2 '14 at 2:38
  • $\begingroup$ @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 (+) ? $\endgroup$ – K-Feldspar Dec 17 '16 at 3:45
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    $\begingroup$ @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 (-). $\endgroup$ – ron Dec 17 '16 at 14:54

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