scholarly journals Hydration dynamics gives the distinctive brown color in the "brown ring" nitrate test

2021 ◽  
Author(s):  
Ambar Banerjee ◽  
Michael R. Coates ◽  
Michael Odelius
Keyword(s):  
Aqueous Solution ◽  
Ab Initio ◽  
Solution Structure ◽  
Ab Initio Molecular Dynamics ◽  
Ring Test ◽  
State Structure ◽  
Structure And Dynamics ◽  
Reference Methods ◽  
Ring Complex ◽  
Dynamics Simulations

The chemistry of the brown-ring test has been investigated for nearly a century. Though recent studies have focused on solid state structure determination and the measurement of spectra, mechanistic details and kinetics, the aspects of solution structure and dynamics remain unknown. From ab initio molecular dynamics simulations of the brown-ring complex in aqueous solution, we have identified that the classically established pseudo-octahedral [Fe(H2O)5(NO)]2+ complex is in equilibrium with a square-pyramidal [Fe(H2O)4(NO)]2+ complex through the exchange of one of the coordinated H2O molecules. We also find, using ab-initio multi-reference methods, that the mixture of these two complexes is what gives the distinctive brown coloration to the brown-ring test. We show that its UV-vis spectrum can be theoretically reproduced only by accounting these two species and not the [Fe(H2O)5(NO)]2+ complex alone. The energetics of the two complexes are also investigated with multi-reference methods.

scholarly journals Hydration dynamics gives the distinctive brown color in the "brown ring" nitrate test

2021 ◽  
Author(s):  
Ambar Banerjee ◽  
Michael R. Coates ◽  
Michael Odelius
Keyword(s):  
Aqueous Solution ◽  
Ab Initio ◽  
Quantum Chemical ◽  
Solution Structure ◽  
Ab Initio Molecular Dynamics ◽  
Ring Test ◽  
Chemical Methods ◽  
Aqua Complexes ◽  
Quantum Chemical Methods ◽  
Ring Complex

The brown ring test is one of the most popular and visually appealing reagent tests, commonly known to chemistry undergrads and familiar even to school students. The exact composition, mechanism and structure of the complex has been investigated for nearly a century. Recent studies have elucidated its UV-vis, EPR and Mossbauer spectra, mechanistic details and kinetics, followed by crystallization and structure determination in solid state. Nonetheless these studies were unable to address the aspects of solution structure and dynamics of the brown ring complex. We have conducted ab initio molecular dynamics simulations of the classic brown ring complex in aqueous solution. In the process from the simulation trajectory, we have identified that the classically established pseudo-octahedral [Fe(H2O)5(NO)]2+ complex is in chemical equilibrium with the square-pyramidal [Fe(H2O)4(NO)]2+ complex through the exchange of one of the coordinated H2O molecules. The dynamics in aqueous solution between the penta-aqua and tetra-aqua complexes in the brown ring system has to our knowledge never been suggested earlier. Interestingly we find, using ab initio multi-reference quantum chemical methods i.e. CASSCF/NEVPT2 and CASPT2 calculations, that the mixture of these two complexes is what gives the distinctive brown coloration to the brown ring test. We show that its UV-vis spectrum can be theoretically reproduced only by accounting these two species, and not solely the classically established [Fe(H2O)5(NO)]2+ complex. The energetics of the penta-aqua and tetra-aqua complexes is also investigated at the level of multi-reference quantum chemical methods.

Electronic Structure and Dynamics of Defect in a-Si:H by Ab-Initio Molecular Dynamics

1993 ◽  
Vol 297 ◽  
Author(s):  
N. Orita ◽  
T. Sasaki ◽  
H. Katayama–Yoshida
Keyword(s):  
Molecular Dynamics ◽  
Electronic Structure ◽  
Ab Initio ◽  
Hydrogenated Amorphous Silicon ◽  
Ab Initio Molecular Dynamics ◽  
Dangling Bond ◽  
Structure And Dynamics ◽  
Dynamics Simulations ◽  
Hydrogenated Amorphous

Electronic structure and dynamics of defects in hydrogenated amorphous silicon (a-Si:H) are investigated based upon ab–initio molecular–dynamics simulations. It is shown that (i) the hydrogen–passivated dangling bond (Si-H), (ii) the positively-ionized three–centered bond (Si– H+–Si), (iii) the negatively–ionized three–coordinated dangling bond (D−) and (iv) the five- coordinated floating bond (F5) are the intrinsic defects in a–Si:H. Based upon the calculated result, we discuss the role of hydrogen and the origin of the photo–induced defect in a-Si:H.

Explaining Asymmetric Solvation of Pt(II) versus Pd(II) in Aqueous Solution Revealed by Ab Initio Molecular Dynamics Simulations

2008 ◽  
Vol 4 (12) ◽  
pp. 2108-2121 ◽  
Author(s):  
Elizabeth C. Beret ◽  
José M. Martínez ◽  
Rafael R. Pappalardo ◽  
Enrique Sánchez Marcos ◽  
Nikos L. Doltsinis ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Aqueous Solution ◽  
Ab Initio ◽  
Molecular Dynamics Simulations ◽  
Ab Initio Molecular Dynamics ◽  
Dynamics Simulations

Protonation-modulated localization of excess electrons in histidine aqueous solutions revealed by ab initio molecular dynamics simulations: anion-centered versus cation-centered localization

2017 ◽  
Vol 19 (21) ◽  
pp. 13807-13818
Author(s):  
Liang Gao ◽  
Yuxiang Bu
Keyword(s):  
Molecular Dynamics ◽  
Aqueous Solution ◽  
Molecular Dynamics Simulation ◽  
Aqueous Solutions ◽  
Ab Initio ◽  
Simulation Study ◽  
Dynamics Simulation ◽  
Ab Initio Molecular Dynamics ◽  
Excess Electrons ◽  
Dynamics Simulations

In this work, we present an ab initio molecular dynamics simulation study on the interaction of an excess electron (EE) with histidine in its aqueous solution.

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