Origin of the optical activity of silver thiogallate

Using a high-accuracy universal polarimeter, the birefringence and optical activity of AgGaS2have been determined between 300 and 500 K. The optical rotation has been found to be 94° mm−1at room temperature for a wavelength of 632.8 nm. This value is unexpectedly small if compared with values close to 1000° mm−1at 485 nm reported previously. The present optical data are well explained using a point-dipole model for the calculation of the refractive indices and optical activity. The main contributors to the optical rotation are the S atoms. However, these atoms are not at positions especially suitable to promote extremely large gyrations. Consequently, the size of the optical rotation reported before in the blue part of the spectrum is presumably due to the existence of a circular dichroism band close to that region. Using an optical system based on a photoelastic modulator, a strong linear dichroism peak has been measured in the range 450–500 nm. This fact has prevented reliable measurement of the circular dichroism.

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DETERMINATION OF THE POLARIZATION OPTICAL PROPERTIES OF THE AMYLOID-CONGO RED COMPLEX BY PHASE MODULATION MICROSPECTROPHOTOMETRY

Journal of Histochemistry & Cytochemistry ◽

10.1177/22.12.1105 ◽

1974 ◽

Vol 22 (12) ◽

pp. 1105-1112 ◽

Cited By ~ 40

Author(s):

DOUGLASS L. TAYLOR ◽

ROBERT D. ALLEN ◽

EARL P. BENDITT

Keyword(s):

Circular Dichroism ◽

Congo Red ◽

Phase Modulation ◽

Optical Rotation ◽

Polarized Light ◽

Visible Spectrum ◽

Linear Dichroism ◽

Cotton Effect ◽

Optical Rotatory Dispersion ◽

Circular Dichroïsm

The polarization properties responsible for the classical "green birefringence" of the amyloid-Congo red complex have been determined by a new optical method, phase modulation microspectrophotometry. This method now makes possible the measurement of one optical property at a time (birefringence, optical rotation, linear dichroism and circular dichroism throughout the visible spectrum) in complex specimens in which visible contrast in polarized light is the result of a mixture of polarization effects. The green birefringence is explained by a combination of optical effects, the strongest of which are dispersion of birefringence and linear dichroism superimposed on the smaller effects of circular dichroism and optical rotatory dispersion. The interaction of the planar dye molecules with the amyloid protein induces an extrinsic Cotton effect.

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Study of chiroptical effects on the novel chiral photonic structure

Multidiscipline Modeling in Materials and Structures ◽

10.1108/mmms-11-2018-0196 ◽

2019 ◽

Vol 16 (3) ◽

pp. 501-507

Author(s):

Chemseddine Zara ◽

Zinelabiddine Mezache ◽

Fatiha Benabdelaziz

Keyword(s):

Circular Dichroism ◽

Photonic Crystal ◽

Optical Activity ◽

Optical Rotation ◽

Wide Frequency Range ◽

Photonic Structure ◽

Small Unit ◽

Chiral Structure ◽

Content Type ◽

Circular Dichroïsm

Purpose The purpose of this paper is to demonstrate a novel chiral photonic crystal with thin thickness and small unit cells via numerical calculations. The multi-band circular dichroism is found in a wide frequency range from 400 to 600 THz by studying the transmission properties. Design/methodology/approach To investigate this chiral photonic structure, refection coefficients are analytically computed using finite element method. Numerical results are given, and physical properties are discussed, including the optical rotation, the circular dichroism and the absorption. Findings The results of this modeling and simulation under COMSOL multiphysics environment have led the authors to study the scattered parameters such as the coefficient of transmission (S21) and the coefficient of reflection (S11) for a 2D CPC nanostructure. The authors have also developed script under the Matlab environment which studies absorption and circular dichroism and ensure the existence of optical activity. According to the obtained results, the coefficient of transmission is proportional to the parameter of chirality. Originality/value The authors have designed a novel chiral photonic structure that exhibits larger circular dichroism. The CD spectrum has typically both positive and negative bands. The design principles defined in this work, which combine the concepts of the photonic crystal with the chiral structure (optical activity, circular dichroism and absorption), represent a model for simulation of the properties of a more complex chiral photonic structure. These results led to realization of novel circularly polarized devices in nanotechnologies.

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Circular dichroism and infrared study of β-turn formation in repeat peptides of elastin

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19871356 ◽

1987 ◽

Vol 52 (5) ◽

pp. 1356-1361

Author(s):

S. Abdel Rahman ◽

M. Elsafty ◽

A. Hattaba

Keyword(s):

Circular Dichroism ◽

Solid State ◽

Ir Spectra ◽

Chain Length ◽

Room Temperature ◽

Infrared Study ◽

Feature Characteristic ◽

C 50 ◽

The Stability ◽

Circular Dichroïsm

The conformation of elastin-like peptides Boc-Ala-Pro-Gly-Val-APEGM, Boc-Ala-Pro-Gly-Val-Gly-Val-APEGM, Boc-Ala-Pro-Gly-Val-Ala-Pro-Gly-Val-Gly-Val-APEGM, Boc-Ala-Pro-Gly-Val-Gly-Val-Ala-Pro-Gly-Val-Gly-Val-APEGM were examined in solution using circular dichroism at 30 °C, 50 °C, and 70 °C and in solid state by IR at room temperature. The studies show that the β-turn is a significant conformational feature for peptides under investigation in solution at 30 °C and 50 °C, but at 70 °C the tetra, hexa, and decapeptides show the CD feature characteristic of the β-structure while the dodecapeptide spectra show the presence of β-turn which indicates the stability of the β-turn at this chain length. The IR spectra show that in the solid state at room temperature all investigated peptides assume essentially a β-turn except the tetrapeptide which present evidence of antiparallel β-structure. The β-turn contribution in the IR spectra increases with the increase of the chain length of the peptide.

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