Chemistry, Department of

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Designs for Donor-Acceptor Copolymer Based Double Heterojunction Solar Cells

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Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-07-10
Abstract: 

Self-consistent field calculations were used to examine a design motif for organic double heterojunction solar cell materials. They are a specific type of cascade heterojunction designed to increase cell voltage without sacrificing current and consist of fully conjugated block polymers. The design employs three sections; a p-type section, an n-type section and a third section called the bridge. The energy alignment between sections is important to optimal device function and a motif based on electron donating and electron accepting subunits was evaluated. If the energetic offset between p-type and n-type sections is greater than the exciton binding energy and if the bridge is formed using the scheme presented, a nearly ideal energetic alignment is obtained. In addition, calculations on the excited states of the system were performed to illustrate the relationship between bridge length and the magnitude of charge carrier recombination currents. An order of magnitude decrease relative to the corresponding diblock polymer can be expected for bridge lengths of > 6 repeat units. Taken in sum, these results offer concrete guidelines for the development of synthetic targets in this promising class of materials.

Document type: 
Article
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Synthesis and Characterization of a Photoaffinity Labelling Probe Based on the Structure of the Cystic Fibrosis Drug Ivacaftor

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-06-15
Abstract: 

Cystic Fibrosis (CF) is a genetic disorder caused by loss-of-function mutations to the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Ivacaftor (1) was the first therapeutic approved for the treatment of CF that is able to restore gating activity to certain CFTR variants although the mechanism of action is poorly understood. Herein we describe the synthesis of a photoaffinity labelling (PAL) probe (2) based on the structure of ivacaftor incorporating a photoreactive diazirine moiety for use in labelling studies designed to identify the binding site for ivacaftor on mutant CFTR. The PAL probe 2 retained potentiation activity, with a potency similar to 1, using a Fluorescent Imaging Plate Reader (FLIPR®) assay measuring ion conductance potentiation of wild type (Wt)-CFTR. Photolabelling experiments with human serum albumin (HSA) as a model protein have shown that probe 2 can label HAS in a manner consistent with observed and predicted binding.

Document type: 
Article

Multifunctional Quinoline-Triazole Derivatives as Potential Modulators of Amyloid-b Peptide Aggregation

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2016-05
Abstract: 

Metal ion dyshomeostasis is hypothesized to play a role in the toxicity and aggregation of the amyloid beta (Aβ) peptide, contributing to Alzheimer's disease (AD) pathology. We report on the synthesis andmetal complexation ability of three bidentate quinoline-triazole derivatives 3-(4-(quinolin-2-yl)-1H-1,2,3-triazol-1-yl)propan-1-ol (QOH), 4-(2-(4-(quinolin-2-yl)-1H-1,2,3-triazol-1-yl)ethyl)morpholine (QMorph), and 4-(2-(4-(quinolin-2-yl)-1H-1,2,3-triazol-1-yl)ethyl)thiomorpholine (QTMorph). We further study the utility of these ligands tomodulate Aβ peptide aggregation processes in the presence and absence of Cu2+ions. Ligand-peptide interactions were first investigated using both 2-D 1H-15N band-selective optimized flip angle short transient heteronuclear multiple quantumcorrelation (SOFAST-HMQC) NMR spectroscopy and molecular modeling techniques, indicating interactionswith glutamic acid (E3) and several residues in the hydrophobic region of Aβ. Native gel electrophoresiswith western blotting along with transmission electron microscopy provided information on the ability of each ligand to modulate Aβ aggregation.While the ligands alone did not modify Aβ peptide aggregation at the 24 h timepoint, signifying relatively weak ligand-peptide interactions, the ligands did modify the aggregation profile of the peptide in the presence of stoichiometric and suprastoichiometric Cu. Interestingly, the thioether derivative QTMorph exhibited the most pronounced effect on peptide aggregation in the presence of Cu. Overall, the quinoline-triazole ligand series were shown to interact with the hydrophobic region of the Aβ peptide, and modulate the Cu-Aβ aggregation process.

Document type: 
Article
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Double layer of Platinum Electrodes: Non-Monotonic Surface Charging Phenomena and Negative Double Layer Capacitance

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-01
Abstract: 

In this study, the refined double layer model of platinum electrodes accounts for chemisorbed oxygen species, oriented interfacial water molecules and ion size effects in solution. It results in a non-monotonic surface charging relation and a peculiar capacitance vs. potential curve with a maximum and maybe negative-defined values in the potential regime of oxide-formation.

 

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Article
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Unifying Theoretical Framework for Deciphering the Oxygen Reduction Reaction on Platinum

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-04-05
Abstract: 

Rapid conversion of oxygen into water is crucial to the operation of polymer electrolyte fuel cells and other emerging electrochemical energy technologies. Chemisorbed oxygen species play double-edged roles in this reaction, acting as vital intermediates on one hand and site-blockers on the other. Any attempt to decipher the oxygen reduction reaction (ORR) must first relate the formation of oxygen intermediates to basic electronic and electrostatic properties of the catalytic surface, and then link it to parameters of catalyst activity. An approach that accomplishes this feat will be of great utility for catalyst materials development and predictive model formulation of electrode operation. Here, we present a theoretical framework for the multiple interrelated surface phenomena and processes involved, particularly, by incorporating the double-layer effects. It sheds light on the roles of oxygen intermediates and gives out the Tafel slope and exchange current density as continuous functions of electrode potential. Moreover, it develops the concept of a rate determining term which should replace the concept of a rate determining step for multi-electron reactions, and offers a new perspective on the volcano relation of the ORR.

 

Document type: 
Article

Chemisorbed Oxygen at Pt(111): a DFT Study of Structural and Electronic Surface Properties

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-11-26
Abstract: 

Simulations based on density functional theory are used to study the electronic and electrostatic properties of a Pt(111) surface covered by a layer of chemisorbed atomic oxygen. The impact of the oxygen surface coverage and orientationally ordered interfacial water layers is explored. The oxygen adsorption energy decreases as a function of oxygen coverage due to the lateral adsorbate repulsion. The surficial dipole moment density induced by the layer of chemisorbed oxygen causes a positive shift of the work function. In simulations with interfacial water layers, ordering and orientation of water molecules strongly affect the work function. It is found that the surficial dipole moment density and charge density are roughly linearly dependent on the oxygen surface coverage. Moreover, we found that water layers exert only a small impact on the surface charging behavior of the surface.

Document type: 
Article

Targeting Therapeutics to Bone by Conjugation with Bisphosphonates

Peer reviewed: 
No, item is not peer reviewed.
Date created: 
2018-04-04
Abstract: 

Bisphosphonates target and bind avidly to the mineral (hydroxyapatite) found in bone. This targeting ability has been exploited to design and prepare bisphosphonate conjugate prodrugs to deliver a wide variety of drug molecules selectively  to bones. It is important that conjugates be stable in the blood stream and that conjugate that is not taken up by bone is eliminated rapidly. The prodrugs should release active drug at a rate appropriate so as to provide efficacy. Radiolabelling is the best method to quantify and evaluate pharmacokinetics, tissue distribution, bone uptake and release of the active drug(s). Recent reports have described bisphosphonate conjugates derived from the antiresorptive drug, alendronic acid and anabolic prostanoid drugs that effectively deliver prostaglandins and prostaglandin EP4 receptor agonists to bone and show enhanced anabolic efficacy and tolerability compared to the drugs alone. These conjugate drugs can be dosed infrequently (weekly or bimonthly) whereas the free drugs must be dosed daily.

Document type: 
Article

Approaching the Self-Consistency Challenge of Electrocatalysis with Theory and Computation

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-04-04
Abstract: 

This opinion piece centers around challenges involved in developing first- principles electrochemical methods. In recent years, theory and computation have become quintessential tools to navigate the parameter space that controls the activity and stability of electrocatalytic materials and electrochemical devices. Viable methods process as input details on materials structure, composition and reaction conditions. Their output includes metrics for stability and activity, phase diagrams, as well as mechanistic insights on reaction mechanisms and pathways. The core challenge, connecting input to output, is a self-consistency problem that couples the electrode potential to variables for the electronic structure of the solid electrode, solvent properties and ion distributions in the electrolyte as well as specific properties of a boundary region in between. We will discuss a theoretical framework and computational approaches that strive to accomplish this feat.

Document type: 
Article

Tipping Water Balance and the Pt Loading Effect in Polymer Electrolyte Fuel Cells: A Model-based Analysis

Peer reviewed: 
Yes, item is peer reviewed.
Abstract: 

The commercial deployment of polymer electrolyte fuel cells (PEFCs) hinges on breakthroughs in design and integration of highly performing and durable catalyst layers with drastically reduced platinum loading. Experimental studies have shown an unexpected increase in voltage losses upon a drastic reduction in the Pt content. In an effort to unravel this peculiar behavior, an existing physical model of catalyst layers in PEFCs is employed to analyze a wide range of fuel cell performance data from the literature. The analysis reveals correlated trends in key fuel cell parameters. These findings can be explained in view of the tipping water balance that affects the interplay of transport and reaction in catalyst layer and gas diffusion media. This represents a compelling alternative to the widespread ionomer-film hypothesis that links observed power losses at low Pt loading to a mesoscopic oxygen transport resistance. The presented theoretical analysis warrants the definition of a correlation exponent that should find use in assessing the merit of different approaches in catalyst layer fabrication.

Document type: 
Article

Morphology of Anion-Conducting Ionenes Investigated by X-ray Scattering and Simulation

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-01-24
Abstract: 

We have studied the morphology of a novel series of benzimidazole-based ionenes, methylated poly(hexamethyl-p-terphenylbenzimidazolium) (HMT-PMBI), in halide form. Materials with anion-exchange capacities ranging from 0 to 2.5 mequiv/g were studied. X-ray scattering reveals three length scales in the materials: ion–polymer spacing (4 Å), polymer–polymer interchain spacing (6 Å), and an intrachain repeat distance (20 Å). No long-range structure is apparent above the monomer length, which is rare in ion-conducting polymer membranes. In preliminary molecular dynamics simulations, water molecules were observed forming chains between ions, even at a modest level of hydration, providing an interpenetrating network where conductivity can occur.

Document type: 
Article