scholarly journals Methyl-Cyclohexane Methanol (MCHM) Isomer-Dependent Binding on Amorphous Carbon Surfaces

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3411
Author(s):  
William A. Alexander
Keyword(s):  
Trans Isomer ◽  
Amorphous Carbon ◽  
Density Functional ◽  
Treatment Plant ◽  
Binding Energies ◽  
Carbon Surface ◽  
Interfacial Chemistry ◽  
Polycyclic Aromatic ◽  
Methyl Cyclohexane ◽  
Chemical Plume

In January 2014, over 10,000 gallons of methyl-cyclohexane methanol (MCHM) leaked into the Elk River in West Virginia, in a chemical spill incident that contaminated a large portion of the state’s water supply and left over 300,000 residents without clean water for many days and weeks. Initial efforts to remove MCHM at the treatment plant centered on the use of granulated activated carbon (GAC), which removed some of the chemical from the water, but MCHM levels were not lowered to a “non-detect” status until well after the chemical plume had moved downstream of the intake. Months later, MCHM was again detected at the outflow (but not the inflow) at the water treatment facility, necessitating the full and costly replacement of all GAC in the facility. The purpose of this study is to investigate the hypothesis that preferential absorbance of one of the two MCHM isomers, coupled with seasonal variations in water temperature, explain this contrary observation. Calculated intermolecular potentials between ovalene (a large planar polycyclic aromatic hydrocarbon) and the MCHM isomers were compared to physisorption potentials of MCHM onto an amorphous carbon model. While a molecular mechanics (MM) force field predicts no difference in the average interaction potentials between the cis- and trans-MCHM with the planar ovalene structure, MM predicts that the trans isomer binds stronger than the cis isomer to the amorphous carbon surface. Semi-empirical and density functional theory also predict stronger binding of trans-MCHM on both the planar and amorphous surfaces. The differences in the isomer binding strengths on amorphous carbon imply preferential absorbance of the trans isomer onto activated charcoal filter media. Considering seasonal water temperatures, simple Arrhenius kinetics arguments based on these predicted binding energies help explain the environmental observations of MCHM leeching from the GAC filters months after the spill. Overall, this work shows the important implications that can arise from detailed interfacial chemistry investigations.

2,2’-Dipyridylamine as Organic Molecular Electrocatalyst for Hydrogen Evolution Reaction in Acidic Electrolytes

2019 ◽  
Author(s):  
Xi Yin ◽  
Ling Lin ◽  
Hoon T. Chung ◽  
Ulises Martinez ◽  
Andrew M. Baker ◽  
...  
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Density Functional ◽  
Low Cost ◽  
Membrane Electrode Assembly ◽  
Carbon Surface ◽  
Membrane Electrode ◽  
Durability Test ◽  
Onset Potential ◽  
Precious Metal Catalysts

Finding a low-cost and stable electrocatalyst for hydrogen evolution reaction (HER) as a replacement for scarce and expensive precious metal catalysts has attracted significant interest from chemical and materials research communities. Here, we demonstrate an organic catalyst based on 2,2’-dipyridylamine (dpa) molecules adsorbed on carbon surface, which shows remarkable hydrogen evolution activity and performance durability in strongly acidic polymer electrolytes without involving any metal. The HER onset potential at dpa adsorbed on carbon has been found to be less than 50 mV in sulfuric acid and in a Nafion-based membrane electrode assembly (MEA). At the same time, this catalyst has shown no performance loss in a 60-hour durability test. The HER reaction mechanisms and the low onset overpotential in this system are revealed based on electrochemical study. Density functional theory (DFT) calculations suggest that the pyridyl-N functions as the active site for H adsorption with a free energy of -0.13 eV, in agreement with the unusually low onset overpotential for an organic molecular catalyst.<br>

2,2’-Dipyridylamine as Organic Molecular Electrocatalyst for Hydrogen Evolution Reaction in Acidic Electrolytes

2019 ◽  
Author(s):  
Xi Yin ◽  
Ling Lin ◽  
Hoon T. Chung ◽  
Ulises Martinez ◽  
Andrew M. Baker ◽  
...  
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Density Functional ◽  
Low Cost ◽  
Membrane Electrode Assembly ◽  
Carbon Surface ◽  
Membrane Electrode ◽  
Durability Test ◽  
Onset Potential ◽  
Precious Metal Catalysts

Finding a low-cost and stable electrocatalyst for hydrogen evolution reaction (HER) as a replacement for scarce and expensive precious metal catalysts has attracted significant interest from chemical and materials research communities. Here, we demonstrate an organic catalyst based on 2,2’-dipyridylamine (dpa) molecules adsorbed on carbon surface, which shows remarkable hydrogen evolution activity and performance durability in strongly acidic polymer electrolytes without involving any metal. The HER onset potential at dpa adsorbed on carbon has been found to be less than 50 mV in sulfuric acid and in a Nafion-based membrane electrode assembly (MEA). At the same time, this catalyst has shown no performance loss in a 60-hour durability test. The HER reaction mechanisms and the low onset overpotential in this system are revealed based on electrochemical study. Density functional theory (DFT) calculations suggest that the pyridyl-N functions as the active site for H adsorption with a free energy of -0.13 eV, in agreement with the unusually low onset overpotential for an organic molecular catalyst.<br>

scholarly journals Exploitation of Baird Aromaticity and Clar’s Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons

Chemistry ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 532-549
Author(s):  
Felix Plasser
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Excited States ◽  
Aromatic Hydrocarbons ◽  
Density Functional ◽  
Materials Science ◽  
Chemical Shifts ◽  
Qualitative Description ◽  
Triplet States ◽  
Excitation Energies ◽  
Polycyclic Aromatic

Polycyclic aromatic hydrocarbons (PAH) are a prominent substance class with a variety of applications in molecular materials science. Their electronic properties crucially depend on the bond topology in ways that are often highly non-intuitive. Here, we study, using density functional theory, the triplet states of four biphenylene-derived PAHs finding dramatically different triplet excitation energies for closely related isomeric structures. These differences are rationalised using a qualitative description of Clar sextets and Baird quartets, quantified in terms of nucleus independent chemical shifts, and represented graphically through a recently developed method for visualising chemical shielding tensors (VIST). The results are further interpreted in terms of a 2D rigid rotor model of aromaticity and through an analysis of the natural transition orbitals involved in the triplet excited states showing good consistency between the different viewpoints. We believe that this work constitutes an important step in consolidating these varying viewpoints of electronically excited states.

scholarly journals Tuning the electronic structure of Ag-Pd alloys to enhance performance for alkaline oxygen reduction

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
José A. Zamora Zeledón ◽  
Michaela Burke Stevens ◽  
G. T. Kasun Kalhara Gunasooriya ◽  
Alessandro Gallo ◽  
Alan T. Landers ◽  
...  
Keyword(s):  
Metal Binding ◽  
Precious Metal ◽  
Metal Content ◽  
Density Functional ◽  
Binding Energies ◽  
Intrinsic Activity ◽  
Energy Technologies ◽  
Highly Active ◽  
Wide Range ◽  
Precious Metal Content

AbstractAlloying is a powerful tool that can improve the electrocatalytic performance and viability of diverse electrochemical renewable energy technologies. Herein, we enhance the activity of Pd-based electrocatalysts via Ag-Pd alloying while simultaneously lowering precious metal content in a broad-range compositional study focusing on highly comparable Ag-Pd thin films synthesized systematically via electron-beam physical vapor co-deposition. Cyclic voltammetry in 0.1 M KOH shows enhancements across a wide range of alloys; even slight alloying with Ag (e.g. Ag0.1Pd0.9) leads to intrinsic activity enhancements up to 5-fold at 0.9 V vs. RHE compared to pure Pd. Based on density functional theory and x-ray absorption, we hypothesize that these enhancements arise mainly from ligand effects that optimize adsorbate–metal binding energies with enhanced Ag-Pd hybridization. This work shows the versatility of coupled experimental-theoretical methods in designing materials with specific and tunable properties and aids the development of highly active electrocatalysts with decreased precious-metal content.

scholarly journals Nanotechnology-based approaches for targeting and delivery of drugs via Hexakis (m-PE) macrocycles

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Samaneh Pasban ◽  
Heidar Raissi
Keyword(s):  
Drug Delivery ◽  
Density Functional ◽  
Water Solution ◽  
Decomposition Analysis ◽  
Binding Energies ◽  
Energy Decomposition Analysis ◽  
Partial Density ◽  
High Propensity ◽  
The Stability ◽  
Novel Applications

AbstractHexakis (m-phenylene ethynylene) (m-PE) macrocycles, with aromatic backbones and multiple hydrogen-bonding side chains, had a very high propensity to self-assemble via H-bond and π–π stacking interactions to form nanotubular structures with defined inner pores. Such stacking of rigid macrocycles is leading to novel applications that enable the researchers to explored mass transport in the sub-nanometer scale. Herein, we performed density functional theory (DFT) calculations to examine the drug delivery performance of the hexakis dimer as a novel carrier for doxorubicin (DOX) agent in the chloroform and water solvents. Based on the DFT results, it is found that the adsorption of DOX on the carrier surface is typically physisorption with the adsorption strength values of − 115.14 and − 83.37 kJ/mol in outside and inside complexes, respectively, and so that the essence of the drug remains intact. The negative values of the binding energies for all complexes indicate the stability of the drug molecule inside and outside the carrier's cavities. The energy decomposition analysis (EDA) has also been performed and shown that the dispersion interaction has an essential role in stabilizing the drug-hexakis dimer complexes. To further explore the electronic properties of dox, the partial density of states (PDOS and TDOS) are calculated. The atom in molecules (AIM) and Becke surface (BS) methods are also analyzed to provide an inside view of the nature and strength of the H-bonding interactions in complexes. The obtained results indicate that in all studied complexes, H-bond formation is the driving force in the stabilization of these structures, and also chloroform solvent is more favorable than the water solution. Overall, our findings offer insightful information on the efficient utilization of hexakis dimer as drug delivery systems to deliver anti-cancer drugs.

scholarly journals A Comparative Study of Oxygen and Hydrogen Adsorption on Strained and Alloy-Supported Pt(111) Monolayers

2021 ◽  
Vol 7 (7) ◽  
pp. 101
Author(s):  
Ian Shuttleworth
Keyword(s):  
Comparative Study ◽  
Density Functional ◽  
Hydrogen Adsorption ◽  
Binding Energies ◽  
High Symmetry ◽  
Density Functionals ◽  
Functional Theory ◽  
Ligand Effects ◽  
Ferromagnetic Alloys ◽  
Depth Study

A comparative study of the unreacted and reacted uniaxially strained Pt(111) and the layered (111)-Pt/Ni/Pt3Ni and (111)-Pt/Ni/PtNi3 surfaces has been performed using density functional theory (DFT). An in-depth study of the unreacted surfaces has been performed to evaluate the importance of geometric, magnetic and ligand effects in determining the reactivity of these different Pt surfaces. An analysis of the binding energies of oxygen and hydrogen over the high-symmetry binding positions of all surfaces has been performed. The study has shown that O and H tend to bind more strongly to the (111)-Pt/Ni/Pt3Ni surface and less strongly to the (111)-Pt/Ni/PtNi3 surface compared to binding on the equivalently strained Pt(111) surfaces. Changes in the surface magnetisation of the surfaces overlaying the ferromagnetic alloys during adsorption are discussed, as well as the behaviour of the d-band centre across all surfaces, to evaluate the potential mechanisms for these differences in binding. An accompanying comparison of the accessible density functionals has been included to estimate the error in the computational binding energies.

A DFT study of spherands containing five anisyl groups — Highly preorganized to bind the alkali metal

2006 ◽  
Vol 84 (8) ◽  
pp. 1045-1049 ◽  
Author(s):  
Shabaan AK Elroby ◽  
Kyu Hwan Lee ◽  
Seung Joo Cho ◽  
Alan Hinchliffe
Keyword(s):  
Density Functional Theory ◽  
Binding Energy ◽  
Density Functional ◽  
Ionic Radius ◽  
Binding Energies ◽  
Cavity Size ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
X Ray ◽  
Good Agreement

Although anisyl units are basically poor ligands for metal ions, the rigid placements of their oxygens during synthesis rather than during complexation are undoubtedly responsible for the enhanced binding and selectivity of the spherand. We used standard B3LYP/6-31G** (5d) density functional theory (DFT) to investigate the complexation between spherands containing five anisyl groups, with CH2–O–CH2 (2) and CH2–S–CH2 (3) units in an 18-membered macrocyclic ring, and the cationic guests (Li+, Na+, and K+). Our geometric structure results for spherands 1, 2, and 3 are in good agreement with the previously reported X-ray diffraction data. The absolute values of the binding energy of all the spherands are inversely proportional to the ionic radius of the guests. The results, taken as a whole, show that replacement of one anisyl group by CH2–O–CH2 (2) and CH2–S–CH2 (3) makes the cavity bigger and less preorganized. In addition, both the binding and specificity decrease for small ions. The spherands 2 and 3 appear beautifully preorganized to bind all guests, so it is not surprising that their binding energies are close to the parent spherand 1. Interestingly, there is a clear linear relation between the radius of the cavity and the binding energy (R2 = 0.999).Key words: spherands, preorganization, density functional theory, binding energy, cavity size.

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