New Developments in Fourier Transform Infrared Vibrational Circular Dichroism Measurements

1989 ◽  
Vol 43 (8) ◽  
pp. 1295-1297 ◽  
Author(s):  
P. L. Polavarapu
Keyword(s):  
Fourier Transform ◽  
Circular Dichroism ◽  
Data Acquisition ◽  
Vibrational Circular Dichroism ◽  
Signal Quality ◽  
New Developments ◽  
Acquisition Period ◽  
Ft Ir ◽  
Circular Dichroïsm ◽  
Special Detector

A new FT-IR vibrational circular dichroism (VCD) spectrometer has been assembled to record VCD spectra with excellent signal quality up to ∼650 cm−1. A special detector with 600 cm−1 cutoff ( D* = 4 × 1010), a ZnSe modulator, and a KRS-5 polarizer were used in these measurements. Typical VCD spectra at 4 cm−1 resolution can be obtained within a one-hour data acquisition period, while those at 1 cm−1 resolution, in the ∼ 1500-650 cm−1 region, can be obtained within four hours of data acquisition per sample. VCD spectra for ã-pinene, 3-bromocamphor, and propylene oxide are presented.

A Solution to the Artifact Problem in Fourier Transform Vibrational Circular Dichroism

1988 ◽  
Vol 42 (1) ◽  
pp. 32-38 ◽  
Author(s):  
Petr Malon ◽  
Timothy A. Keiderling
Keyword(s):  
Fourier Transform ◽  
Circular Dichroism ◽  
Vibrational Circular Dichroism ◽  
Band Shape ◽  
Ft Ir ◽  
Circular Dichroïsm

Using a newly constructed FT-IR vibrational circular dichroism (VCD) instrument, we have found that elimination of the ellipsoidal collection mirror before the detector and its replacement by a lens leads to a significant improvement in the absorption artifact problem seen previously in FT-IR/VCD. In the mid-IR region, we have been able to measure VCD of a single enantiomer for molecules such as α-pinene, 3-methylcyclohexanone, and dimethyltartrate. More importantly, this reduction in artifact level brings the FT-IR/VCD band shape of some particularly-difficult-to-measure bands, such as carbonyl stretches, into better agreement with those found in dispersive measurements. These results imply that the dispersive results are reliable, though of lower resolution than those obtained with the use of FT-IR/VCD.

New Design for Fourier Transform Infrared Vibrational Circular Dichroism Spectrometers

1994 ◽  
Vol 48 (10) ◽  
pp. 1218-1223 ◽  
Author(s):  
Gang-Chi Chen ◽  
Prasad L. Polavarapu ◽  
Stephen Weibel
Keyword(s):  
Fourier Transform ◽  
Circular Dichroism ◽  
Fourier Transform Infrared ◽  
Vibrational Circular Dichroism ◽  
Racemic Mixture ◽  
Area Detector ◽  
Tight Focusing ◽  
Ft Ir ◽  
High Degree ◽  
Circular Dichroïsm

Fourier transform infrared (FT-IR) spectrometers are commonly designed with small-area detectors and tight focusing mirrors. Vibrational circular dichroism (VCD) measurements made with such FT-IR instruments contain polarization artifacts, and VCD measurements on both enantiomers (or one enantiomer and racemic mixture) are required in order to reduce these artifacts. This restriction limits the VCD measurements to only those samples for which both enantiomers (or one enantiomer and racemic mixture) are available. Recently a modified design was reported in the literature where the mirrors between sample and detector were replaced with a BaF2 lens, and a larger-area detector was substituted for the smaller-area counterpart. These modifications successfully alleviated some of the artifact problems. This design, however, is not suitable for polarizing interferometers, where polarizations exiting the interferometer are to be preserved to a high degree of purity. In addition, it is not clear whether the throughput enhancement advantage realized with a larger-area detector completely offsets the disadvantage from increased noise with detector area. Furthermore, BaF2 lenses reduce the broad range routinely available on an FT-IR instrument. Here we report a new design that replaces all the mirrors at the exit port of the interferometer with two KBr lenses and retains the full spectral range (4000–400 cm−1) of mid-infrared FT-IR spectrometers. VCD measurements obtained with small- (1 × 1 mm) and large- (4 × 4 mm) area detectors are found to have similar signal quality.

Step-Scan Fourier Transform Vibrational Circular Dichroism Measurements in the Vibrational Region above 2000 cm−1

1997 ◽  
Vol 51 (4) ◽  
pp. 508-511 ◽  
Author(s):  
Fujin Long ◽  
Teresa B. Freedman ◽  
Thomas J. Tague ◽  
Laurence A. Nafie
Keyword(s):  
Fourier Transform ◽  
Circular Dichroism ◽  
Near Infrared ◽  
Optical Transition ◽  
Signal To Noise Ratio ◽  
Infrared Region ◽  
Vibrational Circular Dichroism ◽  
Ft Ir ◽  
Combination Bands ◽  
Circular Dichroïsm

We present the results of a new Fourier transform infrared vibrational circular dichroism (FT-IR-VCD) spectrometer optimized for performance in the near-infrared region above 2000 cm−1. The instrument is capable of operating in either the conventional rapidscan mode or the step-scan mode and is designed around the Bruker IFS 55 FT-IR spectrometer. We find that in the region of hydrogen stretching, the instrument performs as well as or better than (depending on the spectral coverage and resolution desired) a corresponding dispersive grating VCD spectrometer, with noise levels at approximately 10−6 Δ A units for a two-hour collection at 8-cm−1 resolution. The performance is approximately a factor-of-2 better in signal-to-noise ratio in optimized step-scan operation in comparison to the corresponding results in rapid-scan operation. The reasons are traced to advantages in electronic filtering and undersampling efficiency in step-scan mode. It is expected that the advantages of step-scan will increase with increasing optical transition frequency, such as the region of overtone and combination bands between 4000 and 8000 cm−1.

Design and Performance of an Optimized Dispersive Infrared Dichrograph

1988 ◽  
Vol 42 (1) ◽  
pp. 20-27 ◽  
Author(s):  
M. Diem ◽  
G. M. Roberts ◽  
O. Lee ◽  
A. Barlow
Keyword(s):  
Fourier Transform ◽  
Circular Dichroism ◽  
Data Acquisition ◽  
Vibrational Circular Dichroism ◽  
Electronic Data ◽  
Optical Elements ◽  
And Performance ◽  
Circular Dichroïsm ◽  
Acquisition Method

The design of a spectrometer for the observation of infrared vibrational circular dichroism (VCD) is reported. This instrument utilizes f/4 aperture, a minimum of optical elements, and a new electronic data acquisition method to improve the sensitivity of previous dispersive units. The instrument described exhibits a level of sensitivity comparable to that of present Fourier transform (FT) VCD instruments, while avoiding some problems which still persist in FT-VCD.

Measurement of Vibrational Circular Dichroism Using a Polarizing Michelson Interferometer

1990 ◽  
Vol 44 (1) ◽  
pp. 5-7 ◽  
Author(s):  
N. Ragunathan ◽  
N. S. Lee ◽  
T. B. Freedman ◽  
L. A. Nafie ◽  
C. Tripp ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Circular Dichroism ◽  
Signal To Noise Ratio ◽  
Michelson Interferometer ◽  
Vibrational Circular Dichroism ◽  
Signal To Noise ◽  
Ft Ir ◽  
First Time ◽  
Circular Dichroïsm ◽  
Double Modulation

Fourier transform infrared (FT-IR) vibrational circular dichroism (VCD) has been observed for the first time with the use of a polarizing Michelson interferometer (PMI). VCD spectra have been recorded for (–)- α-pinene between 900 and 1350 cm−1 at 4 cm−1 resolution with excellent signal-to-noise ratio. The FT-VCD spectra are virtually the same as those recorded for (–)- α-pinene under the same conditions with the use of the more conventional double modulation FT-IR approach.

scholarly journals Piscicartone, a Rotenoid From Piscidia carthagenensis

2019 ◽  
Vol 14 (5) ◽  
pp. 1934578X1984979
Author(s):  
Alfredo R. Ortega ◽  
Nury Pérez-Hernández ◽  
Pedro Joseph-Nathan
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Fourier Transform ◽  
Circular Dichroism ◽  
Magnetic Resonance ◽  
Discrete Fourier Transform ◽  
Absolute Configuration ◽  
Vibrational Circular Dichroism ◽  
Magnetic Resonance Studies ◽  
Circular Dichroïsm ◽  
Nuclear Magnetic

The bark of the roots of Piscidia carthagenensis afforded the known insecticides rotenone (1) and millettone (2), as well as the new rotenoid piscicartone (3). The structure of 3 followed from nuclear magnetic resonance studies, while its absolute configuration (AC) was determined by vibrational circular dichroism (VCD) measurements in comparison with discrete Fourier transform B3LYP/DGDZVPcalculated spectra using the Compare VOA software. In addition, the AC of 1 and 2 was verified using the same VCD methodology.

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