scholarly journals Computational Modeling of Chromatin Fiber to Characterize Its Organization Using Angle-Resolved Scattering of Circularly Polarized Light

Polymers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 3422
Author(s):  
Muhammad Waseem Ashraf ◽  
Aymeric Le Gratiet ◽  
Alberto Diaspro
Keyword(s):  
Electromagnetic Scattering ◽  
Structural Parameters ◽  
Polarized Light ◽  
Dipole Approximation ◽  
Chromatin Fiber ◽  
Label Free ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Chiral Polymers ◽  
Nanoscale Level

Understanding the structural organization of chromatin is essential to comprehend the gene functions. The chromatin organization changes in the cell cycle, and it conforms to various compaction levels. We investigated a chromatin solenoid model with nucleosomes shaped as cylindrical units arranged in a helical array. The solenoid with spherical-shaped nucleosomes was also modeled. The changes in chiral structural parameters of solenoid induced different compaction levels of chromatin fiber. We calculated the angle-resolved scattering of circularly polarized light to probe the changes in the organization of chromatin fiber in response to the changes in its chiral parameters. The electromagnetic scattering calculations were performed using discrete dipole approximation (DDA). In the chromatin structure, nucleosomes have internal interactions that affect chromatin compaction. The merit of performing computations with DDA is that it takes into account the internal interactions. We demonstrated sensitivity of the scattering signal’s angular behavior to the changes in these chiral parameters: pitch, radius, the handedness of solenoid, number of solenoid turns, the orientation of solenoid, the orientation of nucleosomes, number of nucleosomes, and shape of nucleosomes. These scattering calculations can potentially benefit applying a label-free polarized-light-based approach to characterize chromatin DNA and chiral polymers at the nanoscale level.

scholarly journals Optical Transition Rates in a Cylindrical Quantum Wire with Parabolic and Inverse Parabolic Electric Confining Potentials in a Magnetic Field

2021 ◽  
Author(s):  
Moletlanyi Tshipa ◽  
Monkami Masale
Keyword(s):  
Magnetic Field ◽  
Applied Magnetic Field ◽  
Polarized Light ◽  
Electronic States ◽  
Dipole Approximation ◽  
Transition Rates ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Quantum Numbers ◽  
Parabolic Potential

Abstract Electron transition rates due to interaction with circularly polarized light incident along the axis of a free-standing solid cylindrical nanowire are evaluated in the dipole approximation. The electric confinement potential of the nanowire is modeled as a superposition of two parts, in general, of different strengths; viz; parabolic and inverse parabolic in the radial distance. Additional confinement of the charge carriers is through the vector potential of the axial applied magnetic field. In systems with cylindrical symmetry, the electronic states are in part characterized by azimuthal quantum numbers: m=0, ±1, ±2,..., which in the absence of the axial applied magnetic field are doubly degenerate. In the dipole approximation and for circularly polarized light the selection rules are such that optical transitions are allowed between electronic states whose azimuthal quantum numbers differ by unity. Transition rates are characterized by peaks whenever the energy of the incident electromagnetic radiation matches transition energies for states between which transitions occur. The parabolic potential blue shifts peak of transition rates while the inverse parabolic potential redshifts the peaks. Results also indicate that transition rates are higher in nanowires of smaller radii. The homogeneous magnetic field lifts the double-degeneracies of electrons with opposite angular momenta, which leads to the emergence of two branches of the transition rates.

Differential polarization imaging of sickled cells

1988 ◽  
Vol 46 ◽  
pp. 62-63
Author(s):  
Marcos F. Maestre
Keyword(s):  
Optical Properties ◽  
Theoretical Approach ◽  
Polarized Light ◽  
Polarization Microscopy ◽  
Spectroscopic Techniques ◽  
Polarization Imaging ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Microscopic Scale ◽  
Chiral Structures

Recently we have developed a form of polarization microscopy that forms images using optical properties that have previously been limited to macroscopic samples. This has given us a new window into the distribution of structure on a microscopic scale. We have coined the name differential polarization microscopy to identify the images obtained that are due to certain polarization dependent effects. Differential polarization microscopy has its origins in various spectroscopic techniques that have been used to study longer range structures in solution as well as solids. The differential scattering of circularly polarized light has been shown to be dependent on the long range chiral order, both theoretically and experimentally. The same theoretical approach was used to show that images due to differential scattering of circularly polarized light will give images dependent on chiral structures. With large helices (greater than the wavelength of light) the pitch and radius of the helix could be measured directly from these images.

Blue Circularly Polarized Luminescent Amorphous Molecules with Single-handed Propeller Chirality Induced by Circularly Polarized Light Irradiation

2021 ◽  
Author(s):  
Zhaoming Zhang ◽  
Takunori Harada ◽  
Adriana Pietropaolo ◽  
Yuting Wang ◽  
Yue Wang ◽  
...  
Keyword(s):  
Polarized Light ◽  
Light Irradiation ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Trigonal Symmetry ◽  
Circularly Polarized Luminescence ◽  
Polarized Luminescence

Preferred-handed propeller conformation was induced by circularly polarized light irradiation to three amorphous molecules with trigonal symmetry, and the molecules with induced chirality efficiently exhibited blue circularly polarized luminescence. In...

scholarly journals Design and Realization of a Compact Efficient Beam Combiner, Based on Liquid Crystal Pancharatnam–Berry Phase Gratings

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 220
Author(s):  
Boxuan Gao ◽  
Jeroen Beeckman ◽  
Kristiaan Neyts
Keyword(s):  
Liquid Crystal ◽  
Berry Phase ◽  
Polarized Light ◽  
Laser Beams ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Beam Combiner ◽  
High Diffraction Efficiency ◽  
High Diffraction ◽  
Crystal Mixture

We demonstrate a laser beam combiner based on four photo-patterned Pancharatnam–Berry (PB) phase gratings, which is compact and has high diffraction efficiency for incident circularly polarized light. The nematic liquid crystal mixture E7 is used as anisotropic material, and the thickness of the layer is controlled by spacers. The beam combiner can bring two parallel laser beams closer to each other while remaining parallel. This work shows the potential to realize components based on flat optical LC devices.

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