Mobility Of Side Chains Research Articles

Dynamics in the Intact fd Bacteriophage Revealed by Pseudo 3D REDOR-Based Magic Angle Spinning NMR.

The development of robust NMR methodologies to probe dynamics on the atomic scale is vital to elucidate the close relations between structure, motion, and function in biological systems. Here, we present an automated protocol to measure, using magic-angle spinning NMR, the effective 13C-15N dipolar coupling constants between multiple spin pairs simultaneously with high accuracy. We use the experimental dipolar coupling constants to quantify the order parameters of multiple C-N bonds in the thousands of identical copies of the coat protein in intact fd-Y21M filamentous bacteriophage virus and describe its overall dynamics on the submillisecond time scale. The method is based on combining three pseudo three-dimensional NMR experiments, where a rotational echo double resonance (REDOR) dephasing block, designed to measure internuclear distances, is combined with three complementary 13C-13C mixing schemes: dipolar-assisted rotational resonance, through-bond transfer-based double quantum/single quantum correlation, and radio frequency driven recoupling. These mixing schemes result in highly resolved carbon spectra with correlations that are created by different transfer mechanisms. We show that the helical part of the coat protein undergoes a uniform small (∼30°) amplitude motion, while the N-terminus is highly flexible. In addition, our results suggest that the reduced mobility of lysine sidechains at the C-terminus are a signature of binding to the single stranded DNA.

Solid-state 13C-NMR spectroscopic determination of side-chain mobilities in zirconium-based metal–organic frameworks

Abstract. Porous interpenetrated zirconium–organic frameworks (PIZOFs) are a class of Zr-based metal–organic frameworks (MOFs) which are composed of long, rod-like dicarboxylate linkers and Zr6O4(OH)4(O2C)12 nodes. Long oligoethylene glycol or aliphatic side chains are covalently attached to the linker molecules in the cases of PIZOF-10 and PIZOF-11, respectively. These side chains are supposedly highly mobile, thus mimicking a solvent environment. It is anticipated that such MOFs could be used as a solid catalyst – the MOF – with pore systems showing properties similar to a liquid reaction medium. To quantify the side-chain mobility, here we have applied different 1D and 2D NMR solid-state spectroscopic techniques like cross-polarization (CP) and dipolar-coupling chemical-shift correlation (DIPSHIFT) studies. The rather high 1H-13C CP efficiency observed for the CH2 groups of the side chains indicates that the long side chains are unexpectedly immobile or at least that their motions are strongly anisotropic. More detailed information about the mobility of the side chains was then obtained from DIPSHIFT experiments. Analytical expressions for elaborate data analysis are derived. These expressions are used to correlate order parameters and to slow motional rates with signals in indirect spectral dimensions, thus enabling the quantification of order parameters for the CH2 groups. The ends of the chains are rather mobile, whereas the carbon atoms close to the linker are more spatially restricted in mobility.

Persistence of Methionine Side Chain Mobility at Low Temperatures in a Nine-Residue Low Complexity Peptide, as Probed by 2 H Solid-State NMR.

Methionine side chains are flexible entities which play important roles in defining hydrophobic interfaces. We utilize deuterium static solid-state NMR to assess rotameric inter-conversions and other dynamic modes of the methionine in the context of a nine-residue random-coil peptide (RC9) with the low-complexity sequence GGKGMGFGL. The measurements in the temperature range of 313 to 161 K demonstrate that the rotameric interconversions in the hydrated solid powder state persist to temperatures below 200 K. Removal of solvation significantly reduces the rate of the rotameric motions. We employed 2 H NMR line shape analysis, longitudinal and rotation frame relaxation, and chemical exchange saturation transfer methods and found that the combination of multiple techniques creates a significantly more refined model in comparison with a single technique. Further, we compare the most essential features of the dynamics in RC9 to two different methionine-containing systems, characterized previously. Namely, the M35 of hydrated amyloid-β1-40 in the three-fold symmetric polymorph as well as Fluorenylmethyloxycarbonyl (FMOC)-methionine amino acid with the bulky hydrophobic group. The comparison suggests that the driving force for the enhanced methionine side chain mobility in RC9 is the thermodynamic factor stemming from distributions of rotameric populations, rather than the increase in the rate constant.

Cellulose nanocrystal stabilized copper nanoparticles for grafting phase change materials with high thermal conductivity

Phase change materials (PCMs) have recently garnered significant attention for thermal energy storage applications. However, widely used PCMs, such as polyethylene glycol (PEG), suffer from low heat conductivity, poor thermal stability, and a tendency to leak, limiting their practical use. Therefore, the objective of this study is to develop a highly thermally conductive composite PCM using PEG and a thermally conductive nanomaterial, specifically cellulose nanocrystals supported by copper nanoparticles (CNC@Cu-NPs). The CNC@Cu-NPs nanocomposite material was used as a matrix to support polyethylene glycol (PEG), resulting in a shape-stable phase change material termed PEG/CNC@Cu-NPs. The obtained PEG/CNC@Cu-NPs were characterized using various analytical techniques. Fourier transform infrared spectroscopy (FTIR) analysis revealed the chemical linkages between PEG and cellulose nanocrystals through a radical polymerization reaction. Polarizing optical microscopy (POM) images of PEG/CNC@Cu-NPs exhibited spherocrystal morphology with smaller sizes compared to pure PEG, suggesting that CNC inhibited PEG side-chain mobility. According to differential scanning calorimetry, the suggested PEG/CNC@Cu-NPs demonstrated a temperature transition between 0.51 °C to 24.5 °C with enthalpies of fusion and crystallization measured at 92.19 and 98.54 J/g, respectively, while also exhibiting excellent cycling stability after 60 heating/cooling cycles. The addition of a modest amount of copper nanoparticles resulted in a remarkable improvement (>50 %) in the thermal conductivity of the PCM. Thermal imaging using an infrared camera showed that PEG/CNC@Cu-NPs exhibited a delay of 10 min in heating compared to pure CNC, confirming the good heat retention capacity of the developed composite material. Based on the aforementioned findings, the proposed PEG/CNC@Cu-NPs PCM offers promising application possibilities in the field of thermal energy storage.

Manipulation of Cationic Group Density in Covalent Organic Framework Membranes for Efficient Anion Transport.

Anion exchange membranes with high anion conductivity are highly desired for electrochemical applications. Increasing ion exchange capacity is a straightforward approach to enhancing anion conductivity but faces a challenge in dimensional stability. Herein, we report the design and preparation of three kinds of isoreticular covalent organic framework (COF) membranes bearing tunable quaternary ammonium group densities as anion conductors. Therein, the cationic groups are integrated into the backbones by flexible ether-bonded alkyl side chains. The highly quaternary ammonium-group-functionalized building units endow COF membranes with abundant cationic groups homogeneously distributed in the ordered channels. The flexible side chains alleviate electrostatic repulsion and steric hindrance caused by large cationic groups, ensuring a tight interlayer stacking and multiple interactions. As a result, our COF membranes achieve a high ion exchange capacity and exceptional dimensional stability simultaneously. Furthermore, the effect of the ionic group density on the ion conductivity in rigid COF channels is systematically explored. Experiments and simulations reveal that the ionic group concentration and side chain mobility jointly determine the ion transport behavior, resulting in the abnormal phenomenon that the anion conductivity is not positively correlated to the ionic group density. The optimal COF membrane achieves the ever-reported highest hydroxide ion conductivity over 300 mS cm-1 at 80 °C and 100% RH. This study offers insightful guidelines on the rational design and preparation of high-performance anion conductors.

Anisotropy in Antimicrobial Bottle Brush Copolymers and Its Influence on Biological Activity

AbstractAntimicrobial polymers are a promising alternative to conventional antibiotics in the fight against antimicrobial resistance. Cationic bottle brush copolymers have shown to be superior to linear topologies in previous studies. Herein, the aspect ratio of such polymers is varied creating differently shaped confined unimolecular structures with varying degrees of side chain mobility. Using reversible addition‐fragmentation chain‐transfer (RAFT) polymerization, bottle brushes are produced in a one‐pot procedure. The morphology is confirmed by atomic force microscopy. The hydrophobicity, as determined via high performance‐liquid chromatography (HPLC) analysis, is drastically influenced by the topology. Using Fourier‐transform infrared (FTIR) spectroscopy, it is found that polymers with a high side chain mobility and increased global hydrophilicity, are less hydrated, and have stronger intramolecular hydrogen bonds. A phase segregated morphology leading to unimolecular micellization is assumed. Biological tests reveal increased antimicrobial activity for such segregated polymers. Their excellent hemocompatibility results in highly selective antimicrobial polymers whose adaptability seems to be a key feature in their excellent performance. This study highlights the tremendous importance of structural control in antimicrobial polymers.

Identification of hydrogen bonding network for proton transfer at the quinol oxidation site of Rhodobacter capsulatus cytochrome bc1

Cytochrome bc1 catalyzes electron transfer from quinol (QH2) to cytochrome c in reactions coupled to proton translocation across the energy-conserving membrane. Energetic efficiency of the catalytic cycle is secured by a two-electron, two-proton bifurcation reaction leading to oxidation of QH2 and reduction of the Rieske cluster and heme bL. The proton paths associated with this reaction remain elusive. Here we used site-directed mutagenesis and quantum mechanical (QM) calculations to analyze the contribution of protonable side chains located at the heme bL side of the quinol oxidation site (Qo) in Rhodobacter capsulatus cytochrome bc1. We observe that the proton path is effectively switched off when H276 and E295 are simultaneously mutated to the non-protonable residues in the H276F/E295V double mutant. The two single mutants, H276F or E295V, are less efficient, but still transfer protons at functionally-relevant rates. Natural selection exposed two single mutations, N279S and M154T, that restored the functional proton transfers in H276F/E295V. QM calculations indicated that H276F/E295V traps the side chain of Y147 in a position distant from QH2, while either N279S or M154T induce local changes releasing Y147 from that position. This shortens the distance between the protonable groups of Y147 and D278 and/or increases mobility of the Y147 side chain, which makes Y147 efficient in transferring protons from QH2 toward D278 in H276F/E295V. Overall, our study identified an extended hydrogen bonding network, build up by E295, H276, D278 and Y147, involved in efficient removal of the proton from QH2 at the heme bL side of Qo.

Properties of hydrated poly(2-methoxyethyl acrylate) observed by 13C-nuclear magnetic resonance spectroscopy

It is well-known that poly(2-methoxyethyl acrylate) (PMEA) exhibits excellent blood compatibility and various investigations have examined the underlying mechanism of this compatibility in terms of the water structure in PMEA and/or inherent PMEA properties. However, information regarding the dynamic properties of the PMEA remains limited. This study was performed to clarify the effect of water molecules on the structure and dynamic properties of hydrated PMEA by comparing dry PMEA using temperature-variable 13C nuclear magnetic resonance spectroscopy (13C-NMR) with a solution probe at 15 –45 °C. Hydration changed the chemical shift values of the four carbons in the PMEA side chain (−COOCH2 CH2OCH3). Investigations of spin-lattice relaxation times and resonance peak widths showed that hydration increased PMEA mobility and the side chain mobility markedly changed at approximately 30 °C, especially in dry PMEA.

A Strategy of Thiolactone Chemistry to Construct Strong and Tough Self-Healing Supramolecular Polyurethane Elastomers via Hierarchical Hydrogen Bonds and Coordination Bonds

Self-healing elastomers with extended service life and enhanced reliability have attracted extensive attention in recent years due to their broad application in fields such as protective coatings, wearable electronics, shape memory materials, and health-care monitoring. However, it is challenging to simultaneously optimize the mechanical properties (strength and toughness) and self-healing capacity of the elastomers. Herein, thiolactone chemistry was delicately used as a bridge to address this conundrum by incorporating 2-ureido-4[1H]-pyrimidinone (UPy) motifs and imidazole ligands into the side chains of linear polyurethane. The synergistic cross-linking of UPy H-bonds and Zn2+-imidazole coordination afforded a robust supramolecular network to significantly improve the strength. Meanwhile, these dynamic cross-linking points acted as sacrificial bonds for energy dissipation under external stress, which played a dominant role in toughening. Therefore, the resultant elastomer (PU-Im-UPy-Zn) exhibited a tensile strength of 9.1 MPa, a breaking elongation of 989%, and toughness up to 62.1 MJ m–3. In addition, the reversible exchange of hierarchical hydrogen bonds (single H-bonds between the carbamate groups and quadruple H-bonds of the UPy dimers) and coordination bonds as well as the high mobility of side chains were conducive to repairing under mild conditions. The superficial scratches completely disappeared at 60 °C, and a satisfactory healing efficiency of 78% was observed after 24 h. This work provides some insights into future design of self-healable supramolecular polyurethane elastomers integrated with conspicuous strength and toughness.

Boronic Ester Transesterification Accelerates Ion Conduction for Comb-like Solid Polymer Electrolytes

Polyether is a kind of ideal polymer matrix for solid polymer electrolytes (SPEs), but its inherent drawbacks (such as the semi-crystalline nature and strong complexation of lithium ions) still hinder their commercial application. The construction of comb-like SPEs effectively increases their functionalities and improves the comprehensive performance. Herein, we apply a dynamic boronic ester exchange strategy to simultaneously enhance the lithium-ion conduction and self-healing ability of the SPEs, thus effectively solving the current problems of polyether. The copolymer (GPA) containing side chains with poly(ethylene glycol) (PEG) and diol groups was obtained through reversible addition–fragmentation chain-transfer (RAFT) polymerization and hydrolysis, and PBA-M2070 containing the boronic acid group and flexible polyether segments was obtained via Schiff base reaction. Boronic ester bonds were formed by dehydration of the diol groups of GPA and the boronic acid groups of PBA-M2070. Dynamic exchange of the boronic ester bonds at the branched sites enhanced the side-chain motion, thus increasing the self-healing ability and electrochemical performance of the SPEs, as well as the cycling stability of assembled batteries. Benefiting from the dynamic boronic ester exchange and enhanced side-chain mobility, the SPEs exhibited self-healing within 10 min and an ionic conductivity of 1.58 × 10–5 S cm–1 at 30 °C. The assembled lithium metal batteries (LMBs) were operated stably at 0.5C for 300 cycles. The dynamic boronic ester exchange strategy used to enhance the LMBs properties provides new insight into the design of comb-like polymer electrolytes.

Positron annihilation lifetime spectroscopic analysis of Nafion and graft‐type polymer electrolyte membranes for fuel cell application

AbstractThe subnano free‐volume hole features of Nafion‐212 and poly(styrene sulfonic acid) grafted poly(ethylene‐co‐tetrafluoroethylene) polymer electrolyte membranes are investigated by using the positron annihilation lifetime spectroscopic analyses with three‐ and four‐component models (i.e., one‐ and two‐ortho‐positronium [o‐Ps] components). The four‐component model provides a more adequate description of free‐volume hole features for both membranes, in which the longer o‐Ps lifetime is assigned to the larger free volume hole sizes in the mobile side chains, while the shorter o‐Ps lifetime is associated with the smaller free volume hole sizes within the backbones (the rigid amorphous fractions and the crystalline‐amorphous interfaces) and the interfaces between the main chains and the side chains. The o‐Ps annihilation is found to occur primarily in the side chains. The subnano volume hole features revealed by the positron annihilation lifetime (PAL) spectra suggest the primary water uptake and conductance in the side chains and the possible presence of water molecules in the rigid amorphous fractions and the interfaces. Note that the three‐component model as usually reported in the literature may underestimate the lifetime and intensity of ortho‐positronium annihilation.

Proton TOCSY NMR relaxation rates quantitate protein side chain mobility in the Pin1 WW domain

Protein side chain dynamics play a vital role in many biological processes, but differentiating mobile from rigid side chains remains a technical challenge in structural biology. Solution NMR spectroscopy is ideally suited for this but suffers from limited signal-to-noise, signal overlap, and a need for fractional 13C or 2H labeling. Here we introduce a simple strategy measuring initial 1H relaxation rates during a 1H TOCSY sequence like DIPSI-2, which can be appended to the beginning of any multi-dimensional NMR sequence that begins on 1H. The TOCSY RF field compels all 1H atoms to behave similarly under the influence of strong coupling and rotating frame cross-relaxation, so that differences in relaxation rates are due primarily to side chain mobility. We apply the scheme to a thermostable mutant Pin1 WW domain and demonstrate that the observed 1H relaxation rates correlate well with two independent NMR measures of side-chain dynamics, cross-correlated 13C relaxation rates in 13CβH2 methylene groups and maximum observable 3J couplings sensitive to the χ1 side chain dihedral angle (3JHα,Hβ, 3JN,Hβ, and 3JCO,Hβ). The most restricted side chains belong to Trp26 and Asn40, which are closely packed to constitute the folding center of the WW domain. None of the other conserved aromatic residues is as immobile as the first tryptophan side chain of the WW domain. The proposed 1H relaxation methodology should make it relatively easy to measure side chain dynamics on uniformly 15N- or 13C-labeled proteins, so long as chemical shift assignments are obtainable.

Development of highly alkaline stable anion conductive polymers with fluorene backbone for water electrolysis

AbstractAnion exchange membrane water electrolysis (AEMWE) is currently paying attention as a new hydrogen (H2) production method since it can operate at high current densities using inexpensive nonnoble metal catalysts. However, the significant problems of AEMs, including their insufficient anion conductivity and alkaline stability, prevent the practical usage of AEMWE. We show a novel anion conductive polymer, alkyl trimethylammonium‐substituted polyfluorene (TMA‐PF), bearing no heteroatom bonds in the main chain. The TMA‐PF membrane possesses higher anion conductivity than conventional AEMs due to the increased flexibility and mobility of the alkylammonium side chains of TMA‐PF. The TMA‐PF membrane shows high‐alkaline stability and maintains the initial ion conductivity after immersion in an aqueous NaOH solution (8 mol L−1) at 80°C for 48 h. In the water electrolysis evaluation, the cell using the TMA‐PF membrane exhibits a higher current density (400 mA cm−2 at 2.03 V) than the cell using the conventional AEM at the same potential, indicating that the novel AEM has a high potential to generate H2 effectively. Green hydrogen produced by AEMWE using renewable energy will be an environmentally benign energy source without CO2 emissions.

Molecular Dynamics Study of Reaction Conditions at Active Catalyst-Ionomer Interfaces in Polymer Electrolyte Fuel Cells

Understanding the local reaction conditions at the catalyst-ionomer interfaces inside of polymer electrolyte fuel cells is vital for improving cell performance and stability. Properties of the water film and distributions of protons and oxygen molecules at the catalyst-ionomer interface are affected by the state of the catalyst and support surfaces and the structure of the ionomer skin layer. In this work, the interfacial region between catalyst and support surface and ionomer skin is simulated using molecular dynamics. This water-filled nanopore model is constructed to study the impact of local charge density, density of sidechains at the ionomer layer, and water layer thickness on the water structure and electrostatic conditions in the pore as well as the transport properties of water, hydronium, and molecular oxygen at the interface. The analysis of the flooded pore model indicates that surface hydrophilicity, represented by water adsorption and the formation of an ordered water layer at the surface, is a major factor determining the interfacial proton density, ionomer sidechain mobility, and interfacial oxygen transport resistance. The results obtained can guide the design of new catalyst materials, where the hydrophilicity of the surface can be tailored to minimize the local proton transport resistance and improve electrode performance.

Is Cys(MTSL) the Best α-Amino Acid Residue to Electron Spin Labeling of Synthetically Accessible Peptide Molecules with Nitroxides?

Electron paramagnetic resonance spectroscopy, particularly its pulse technique double electron–electron resonance (DEER) (also termed PELDOR), is rapidly becoming an extremely useful tool for the experimental determination of side chain-to-side chain distances between free radicals in molecules fundamental for life, such as polypeptides. Among appropriate probes, the most popular are undoubtedly nitroxide electron spin labels. In this context, suitable biosynthetically derived, helical regions of proteins, along with synthetic peptides with amphiphilic properties and antibacterial activities, are the most extensively investigated compounds. A strict requirement for a precise distance measurement has been identified in a minimal dynamic flexibility of the two nitroxide-bearing α-amino acid side chains. To this end, in this study, we have experimentally compared in detail the side-chain mobility properties of the two currently most widely utilized residues, namely, Cys(MTSL) and 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC). In particular, two double-labeled, chemically synthesized 20-mer peptide molecules have been adopted as appropriate templates for our investigation on the determination of the model intramolecular separations. These double-Cys(MTSL) and double-TOAC compounds are both analogues of the almost completely rigid backbone peptide ruler which we have envisaged and 3D structurally analyzed as our original, unlabeled compound. Here, we have clearly found that the TOAC side-chain labels are largely more 3D structurally restricted than the MTSL labels. From this result, we conclude that the TOAC residue offers more precise information than the Cys(MTSL) residue on the side chain-to-side chain distance distribution in synthetically accessible peptide molecules.

Use of Site-Directed Spin Labeling EPR Spectroscopy to Study Protein-LPS Interactions.

Site-directed spin labeling EPR (electron paramagnetic resonance) spectroscopy is a technique used to identify the local conformational changes at a specific residue of interest within a purified protein in response to a ligand. Here, we describe the site-directed spin labeling EPR spectroscopy methodology to monitor changes in the side-chain motion in soluble lipopolysaccharide transport proteins upon the addition of lipopolysaccharide (LPS). A comparison of the spectral overlays of the spin-labeled protein in the absence and presence of LPS provides a qualitative visualization of how LPS binding affects the motion of each spin-labeled site tested within the protein. No change in the spectral lineshapes of a spin-labeled protein in the absence and presence of LPS indicates that the site is not affected by LPS binding, while differences in the spectral lineshapes indicate that LPS does affect the mobility of the spin label side chain within the protein structure. This is a powerful readout of conformational changes at specific residues of interest that can be used to identify a specific site as a reporter of changes induced by ligand binding and to map out the effects of ligand binding through an array of reporter sites within a protein. With the use of AquaStar tubing, protein concentrations as low as 2μM allow for up to a 100-fold excess of LPS. This methodology may also be applied to other protein-ligand or protein-protein interactions with minor adaptations.

Modeling a unit cell: crystallographic refinement procedure using the biomolecular MD simulation platform Amber.

A procedure has been developed for the refinement of crystallographic protein structures based on the biomolecular simulation program Amber. The procedure constructs a model representing a crystal unit cell, which generally contains multiple protein molecules and is fully hydrated with TIP3P water. Periodic boundary conditions are applied to the cell in order to emulate the crystal lattice. The refinement is conducted in the form of a specially designed short molecular-dynamics run controlled by the Amber ff14SB force field and the maximum-likelihood potential that encodes the structure-factor-based restraints. The new Amber-based refinement procedure has been tested on a set of 84 protein structures. In most cases, the new procedure led to appreciably lower R free values compared with those reported in the original PDB depositions or obtained by means of the industry-standard phenix.refine program. In particular, the new method has the edge in refining low-accuracy scrambled models. It has also been successful in refining a number of molecular-replacement models, including one with an r.m.s.d. of 2.15 Å. In addition, Amber-refined structures consistently show superior MolProbity scores. The new approach offers a highly realistic representation of protein-protein interactions in the crystal, as well as of protein-water interactions. It also offers a realistic representation of protein crystal dynamics (akin to ensemble-refinement schemes). Importantly, the method fully utilizes the information from the available diffraction data, while relying on state-of-the-art molecular-dynamics modeling to assist with those elements of the structure that do not diffract well (for example mobile loops or side chains). Finally, it should be noted that the protocol employs no tunable parameters, and the calculations can be conducted in a matter of several hours on desktop computers equipped with graphical processing units or using a designated web service.

Impact of Surface Hydrophilicity on Structure and Transport at the Catalyst-Ionomer Interface: Insights from Molecular Dynamics

Understanding local reaction conditions at the catalyst/support-ionomer interface in the cathode catalyst layer of polymer electrolyte fuel cells is vital for improving cell performance and stability.1 The structure of the ionomer layer and the state of the catalyst support surface at the interface affects key properties of the system, such as water film structure and the distribution of protons and oxygen molecules at the catalyst-ionomer interface.2 The effect of catalyst surface facet and oxidation on the proton density accumulation at the interface was previously studied using molecular dynamics simulations.3 In this work, the interfacial region between catalyst and support surface and ionomer skin is further studied by expanding the classical molecular dynamics model. This water-filled nanopore model is constructed to study the impact of local charge density distribution, density of sidechains at the ionomer layer, and water layer thickness on equilibrium water structure, electrostatic conditions, and transport properties of water, hydronium, and molecular oxygen at the interface (Figure 1). Structural properties of the catalyst and support surfaces are obtained from explicit quantum mechanical Density Functional Theory simulations, and the effect of the electrode potential is simulated via surface charge density by varying the oxide coverage of both C and Pt. The analysis of simulations in a flooded pore indicates that surface hydrophilicity, which is represented by water adsorption and the formation of ice-like water clusters at the surface, is a major deterministic factor that affects interfacial proton density, ionomer sidechain mobility, and interfacial oxygen lateral movement. The results obtained in this work can guide the design of new catalyst materials, where the hydrophilicity of the surface can be tailored to minimize local proton transport resistance and improve electrode performance.Figure 1. Snapshot of the model system with the graphite slab partially covered by epoxide with a C/O ration of 4:1 as the support surface, and a Nafion skin layer of 1124 EW as the ionomer. Li, H.; Tang, Y.; Wang, Z.; Shi, Z.; Wu, S.; Song, D.; Zhang, J.; Fatih, K.; Zhang, J.; Wang, H.; Liu, Z.; Abouatallah, R.; Mazza, A., A review of water flooding issues in the proton exchange membrane fuel cell. Journal of Power Sources 2008, 178 (1), 103-117. Jahnke, T.; Futter, G.; Latz, A.; Malkow, T.; Papakonstantinou, G.; Tsotridis, G.; Schott, P.; Gérard, M.; Quinaud, M.; Quiroga, M.; Franco, A. A.; Malek, K.; Calle-Vallejo, F.; Ferreira de Morais, R.; Kerber, T.; Sautet, P.; Loffreda, D.; Strahl, S.; Serra, M.; Polverino, P.; Pianese, C.; Mayur, M.; Bessler, W. G.; Kompis, C., Performance and degradation of Proton Exchange Membrane Fuel Cells: State of the art in modeling from atomistic to system scale. Journal of Power Sources 2016, 304, 207-233. Spooner, J. A.; Eslamibidigoli, M. J.; Malek, K.; Eikerling, M., Molecular Dynamics Study of the Nanoscale Proton Density Distribution at the Ionomer-Catalyst Interface. Pacific RIM Meeting on Electrochemical and Solid State Science 2020, (I01A-2101). Figure 1

Structure and Function of Bottlebrush Polymer: [i] Control of Confirmation by Stiff Main Chain and [ii] Anchoring Properties of Liquid Crystal Determined by Mobility of Side Chain

Structure and Function of Bottlebrush Polymer: [i] Control of Confirmation by Stiff Main Chain and [ii] Anchoring Properties of Liquid Crystal Determined by Mobility of Side Chain

Investigation of Structural Dynamics of the KCNE3 in a Lipid Bilayer Membrane using Site-Directed Spin Labeling EPR Spectroscopy

KCNE3, a single pass membrane protein, is responsible for controlling the function of multiple potassium channels, one of which is the KCNQ1 channel. The binding of KCNE3 with KCNQ1 is vital in transepithelial potassium ion recycling which has been associated with disorders such as cystic fibrosis. Although KCNE3 has great biological significance, its structural and dynamic information in a native like environment is poorly understood. In this study, we have utilized site-directed spin labeling electron paramagnetic resonance (SDSL-EPR) spectroscopic technique to investigate structural dynamics of KCNE3 in lipid bilayers. KCNE3 was overexpressed and purified in LMPG detergent micelles. MTSL spin label was introduced followed by the incorporation of the protein into POPC/POPG lipid bilayer. Continuous wave (CW)-EPR spectral lineshape analysis was performed on several spin labeling sites including transmembrane domain and extracellular domain of KCNE3 in LMPG detergent micelles and POPC/POPG lipid bilayes to obtain the spin label sidechain mobility and the rotational correlation times. Our EPR data indicated that the nitroxide spin label sidechains in liposomes have slower motion for the sites in the transmembrane domain of KCNE3 when compared to that in the extracellular region of KCNE3. Our results are consistent with the previously published solution NMR structure of KCNE3.