Effect of monovalent and divalent ionic environment on the in-lattice nanoparticle-grafted single-stranded DNA

Soft Matter ◽  
2021 ◽  
Author(s):  
Sunita Srivastava ◽  
Anuj Chhabra ◽  
Oleg Gang
Keyword(s):  
Single Stranded Dna ◽  
Ionic Environment ◽  
Counter Ions ◽  
Complex Manner

The polyelectrolyte (PE) chains respond in a complex manner to the multivalent salt environments, and this behavior depends on pH, temperature, and the presence of specific counter ions. Although much...

Conformational characterization of nucleosome structure by Electron Microscopy

1993 ◽  
Vol 51 ◽  
pp. 194-195
Author(s):  
Gregory J. Czarnota
Keyword(s):  
Electron Microscopy ◽  
Structural Changes ◽  
Physiological State ◽  
Gene Activation ◽  
Three Dimensional ◽  
Macromolecular Complex ◽  
Ultrastructural Studies ◽  
Ionic Environment ◽  
Nucleosome Structure ◽  
Dimensional Reconstruction

Chromatin structure at the fundamental level of the nucleosome is important in vital cellular processes. Recent biochemical and genetic analyses show that nucleosome structure and structural changes are very active participants in gene expression, facilitating or inhibiting transcription and reflecting the physiological state of the cell. Structural states and transitions for this macromolecular complex, composed of DNA wound about a heterotypic octamer of variously modified histone proteins, have been measured by physico-chemical techniques and by enzyme-accessibility and are recognized to occur with various post-translational modifications, gene activation, transformation and with ionic-environment. In spite of studies which indicate various forms of nucleosome structure, all current x-ray and neutron diffraction studies have consistently resulted in only one structure, suggestive of a static conformation. In contrast, two-dimensional electron microscopy studies and three-dimensional reconstruction techniques have yielded different structures. These fundamental differences between EM and other ultrastructural studies have created a long standing quandary, which I have addressed and resolved using spectroscopic electron microscopy and statistical analyses of nucleosome images in a study of nucleosome structure with ionic environment.

Intrinsic doping limit and defect-assisted luminescence in Cs4PbBr6

2019 ◽  
Author(s):  
Young-Kwang Jung ◽  
Joaquin Calbo ◽  
Ji-Sang Park ◽  
Lucy D. Wahlley ◽  
Sunghyun Kim ◽  
...  
Keyword(s):  
First Principles ◽  
Room Temperature ◽  
Stokes Shift ◽  
Green Luminescence ◽  
Counter Ions ◽  
Self Consistent ◽  
Deep Ultraviolet ◽  
Halide Perovskite ◽  
Related Compounds ◽  
Level Analysis

Cs<sub>4</sub>PbBr<sub>6 </sub>is a member of the halide perovskite family that is built from isolated (zero-dimensional) PbBr<sub>6</sub><sup>4-</sup> octahedra with Cs<sup>+</sup> counter ions. The material exhibits anomalous optoelectronic properties: optical absorption and weak emission in the deep ultraviolet (310 - 375 nm) with efficient luminescence in the green region (~ 540 nm). Several hypotheses have been proposed to explain the giant Stokes shift including: (i) phase impurities; (ii) self-trapped exciton; (iii) defect emission. We explore, using first-principles theory and self-consistent Fermi level analysis, the unusual defect chemistry and physics of Cs<sub>4</sub>PbBr<sub>6</sub>. We find a heavily compensated system where the room-temperature carrier concentrations (< 10<sup>9</sup> cm<sup>-3</sup>) are more than one million times lower than the defect concentrations. We show that the low-energy Br-on-Cs antisite results in the formation of a polybromide (Br<sub>3</sub>) species that can exist in a range of charge states. We further demonstrate from excited-state calculations that tribromide moieties are photoresponsive and can contribute to the observed green luminescence. Photoactivity of polyhalide molecules is expected to be present in other halide perovskite-related compounds where they can influence light absorption and emission. <br>

Intrinsic doping limit and defect-assisted luminescence in Cs4PbBr6

2019 ◽  
Author(s):  
Young-Kwang Jung ◽  
Joaquin Calbo ◽  
Ji-Sang Park ◽  
Lucy D. Wahlley ◽  
Sunghyun Kim ◽  
...  
Keyword(s):  
First Principles ◽  
Room Temperature ◽  
Stokes Shift ◽  
Green Luminescence ◽  
Counter Ions ◽  
Self Consistent ◽  
Deep Ultraviolet ◽  
Halide Perovskite ◽  
Related Compounds ◽  
Level Analysis

Cs<sub>4</sub>PbBr<sub>6 </sub>is a member of the halide perovskite family that is built from isolated (zero-dimensional) PbBr<sub>6</sub><sup>4-</sup> octahedra with Cs<sup>+</sup> counter ions. The material exhibits anomalous optoelectronic properties: optical absorption and weak emission in the deep ultraviolet (310 - 375 nm) with efficient luminescence in the green region (~ 540 nm). Several hypotheses have been proposed to explain the giant Stokes shift including: (i) phase impurities; (ii) self-trapped exciton; (iii) defect emission. We explore, using first-principles theory and self-consistent Fermi level analysis, the unusual defect chemistry and physics of Cs<sub>4</sub>PbBr<sub>6</sub>. We find a heavily compensated system where the room-temperature carrier concentrations (< 10<sup>9</sup> cm<sup>-3</sup>) are more than one million times lower than the defect concentrations. We show that the low-energy Br-on-Cs antisite results in the formation of a polybromide (Br<sub>3</sub>) species that can exist in a range of charge states. We further demonstrate from excited-state calculations that tribromide moieties are photoresponsive and can contribute to the observed green luminescence. Photoactivity of polyhalide molecules is expected to be present in other halide perovskite-related compounds where they can influence light absorption and emission. <br>

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