Universal spectropolarimeter based on overtone circular dichroism measurements in the near-infrared region.
A novel and highly sensitive circular dichroism spectropolarimeter for the near-infrared region has been developed. In this instrument, a solid state titanium-sapphire laser that can be spectrally tuned from 670 to 1030 nm was used as the light source. The laser beam was converted into linearly polarized light by a polarizer and into left circularly polarized light and right circularly polarized light at 42 kHz by a photoelastic modulator (PEM). A limit of detection of 1.1 x 10(-6) AU was achieved by this instrument for (+)-Co(en)3(3+) at 765 nm. Further improvement including employing double modulation (at 42 kHz by the PEM and at 85 Hz by a chopper just before the laser beam was converted to CPL), demodulating and amplifying the signal with high-performance lock-in amplifiers, was made to enable the instrument to have the required sensitivity for the measurements of the circular dichroism of overtones and combination transitions of saturated chiral compounds, e.g., (R)- and (S)-camphor, (R)- and (S)-2-octanol, and (R)- and (S)-2-amino-1-octanol. Because the measured CD spectra originate from the overtones and combination transitions of the C-H and O-H groups, the spectropolarimeter can be used to detect virtually any compounds that have O-H and/or C-H groups.
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Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53233.
Grishko
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D000537:Aluminum Oxide / Q000737:chemistry; D000605:Amino Alcohols / Q000032:analysis; D002164:Camphor / Q000032:analysis; D002942:Circular Dichroism; D007834:Lasers; D000442:Octanols / Q000032:analysis; D013055:Spectrophotometry, Infrared; D013237:Stereoisomerism; D014025:Titanium / Q000737:chemistry
D000605:Amino Alcohols; D000442:Octanols; C067943:2-octanol; D002164:Camphor; D014025:Titanium; D000537:Aluminum Oxide; C006506:2-amino-1-butanol