Cation Bridging Studied by Specular Neutron Reflection

Wang, Xiaofan; Lee, Seung Yeon; Miller, Kathy; Welbourn, Rebecca J. L.; Stocker, Isabella; Clarke, Stuart M.; Casford, Michael T. L.; Gutfreund, Philipp; Skoda, Maximilian W. A.

doi:10.1021/la400767u

Cited by 56 publications

(81 citation statements)

References 62 publications

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“…The high concentration required suggests unspecific shielding of close opposing charges at both sides of the domain interface. Similar behaviour has been reported for surfactants, DNA and hyaluronan in the presence of Ca 2+ , and was termed the ‘divalent cation bridging effect’ .…”

Section: Resultssupporting

confidence: 64%

Inter‐domain electron transfer in cellobiose dehydrogenase: modulation by pH and divalent cations

et al. 2015

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The flavocytochrome cellobiose dehydrogenase (CDH) is secreted by wood-decomposing fungi, and is the only known extracellular enzyme with the characteristics of an electron transfer protein. Its proposed function is reduction of lytic polysaccharide mono-oxygenase for subsequent cellulose depolymerization. Electrons are transferred from FADH2 in the catalytic flavodehydrogenase domain of CDH to haem b in a mobile cytochrome domain, which acts as a mediator and transfers electrons towards the active site of lytic polysaccharide mono-oxygenase to activate oxygen. This vital role of the cytochrome domain is little understood, e.g. why do CDHs exhibit different pH optima and rates for inter-domain electron transfer (IET)? This study uses kinetic techniques and docking to assess the interaction of both domains and the resulting IET with regard to pH and ions. The results show that the reported elimination of IET at neutral or alkaline pH is caused by electrostatic repulsion, which prevents adoption of the closed conformation of CDH. Divalent alkali earth metal cations are shown to exert a bridging effect between the domains at concentrations of > 3 mm, thereby neutralizing electrostatic repulsion and increasing IET rates. The necessary high ion concentration, together with the docking results, show that this effect is not caused by specific cation binding sites, but by various clusters of Asp, Glu, Asn, Gln and the haem b propionate group at the domain interface. The results show that a closed conformation of both CDH domains is necessary for IET, but the closed conformation also increases the FAD reduction rate by an electron pulling effect.

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Section: Resultssupporting

confidence: 64%

Inter‐domain electron transfer in cellobiose dehydrogenase: modulation by pH and divalent cations

et al. 2015

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“…Other researchers have discovered that AOT has a high affinity for charged surfaces-even like-charged surfaces-in the presence of divalent cations. 25 This enhanced absorption has been attributed to "cation-bridging", where two AOT molecules become associated with each divalent cation, typically in aqueous solutions at high pH. AOT adsorbs onto the surface, creating a lamellar phase that can assist in the dissolution of minerals by cation exchange.…”

Section: Resultsmentioning

confidence: 99%

Phase pure α-Mn₂O₃ prisms and their bifunctional electrocatalytic activity in oxygen evolution and reduction reactions

2016

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Synthesizing manganese oxide materials with exact control of the nanoparticle shape and phase is difficult, making it challenging to understand the influence of the surface structure on electrocatalysis. Here we describe an inexpensive, low-temperature method to synthesize single-crystal orthorhombic phase α-MnO prisms bound by the {100} facets. The synthesis is the first method to use the cation bridging effect to assist in the creation of α-MnO prisms. According to structural analysis using X-ray diffraction, X-ray pair-distribution function (PDF) measurements and high resolution transmission electron microscopy, the material is composed exclusively of α-MnO prisms, and no additional amorphous or nanocrystalline phases are present. Heating the prisms transformed the material to a more symmetrical, cubic phase α-MnO that exhibited strong bifunctional electrocatalytic activity for the oxygen evolution (OER) and oxygen reduction (ORR) reactions. We compared the oxygen electrode activities (OEA) and found that the α-MnO prisms performed 79% better than commercially-produced α-MnO powders, indicating that these α-MnO prisms perform well as inexpensive, earth-abundant materials for reversible electrodes.

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“…Adsorption of NaAOT and Ca(AOT) 2 salts on other mineral surfaces at the CMC (sapphire, calcite, silica) has been reported as a single bilayer 6,10,11 . The unusual 3 ′ and 4 ′ structures appear specific to the mica surface in combination with the Ca(AOT) 2 salt.…”

Section: Multilayers Of Ca(aot)mentioning

confidence: 99%

Multilayering of Calcium Aerosol-OT at the Mica/Water Interface Studied with Neutron Reflection: Formation of a Condensed Lamellar Phase at the CMC

et al. 2016

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Using specular neutron reflection, the adsorption of sodium and calcium salts of the surfactant bis(2-ethylhexyl) sulfosuccinate (Aerosol-OT or AOT) has been studied at the mica/water interface at concentrations between 0.1 and 2 CMC. The pH dependence of the adsorption was also probed. No evidence of the adsorption of Na(AOT) was found even at the critical micelle concentration (CMC) while the calcium salt was found to adsorb significantly at concentrations of 0.5 CMC and above. This interesting and somewhat unexpected finding demonstrates that counterion identity may be used to tune the adsorption of anionic surfactants on anionic surfaces. At the CMC, three condensed bilayers of Ca(AOT) were adsorbed at pH 7 and 9 and four bilayers adsorbed at pH 4. Multilayering at the CMC of Ca(AOT) on the mica surface is an unusual feature of this surfactant/surface combination. Only single bilayer adsorption has been observed at other surfaces at the CMC. We suggest this arises from the high charge density of mica which must provide an excellent template for the surfactant.

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Cation Bridging Studied by Specular Neutron Reflection

Cited by 56 publications

References 62 publications

Inter‐domain electron transfer in cellobiose dehydrogenase: modulation by pH and divalent cations

Inter‐domain electron transfer in cellobiose dehydrogenase: modulation by pH and divalent cations

Phase pure α-Mn₂O₃ prisms and their bifunctional electrocatalytic activity in oxygen evolution and reduction reactions

Multilayering of Calcium Aerosol-OT at the Mica/Water Interface Studied with Neutron Reflection: Formation of a Condensed Lamellar Phase at the CMC

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Cation Bridging Studied by Specular Neutron Reflection

Cited by 56 publications

References 62 publications

Inter‐domain electron transfer in cellobiose dehydrogenase: modulation by pH and divalent cations

Inter‐domain electron transfer in cellobiose dehydrogenase: modulation by pH and divalent cations

Phase pure α-Mn2O3 prisms and their bifunctional electrocatalytic activity in oxygen evolution and reduction reactions

Multilayering of Calcium Aerosol-OT at the Mica/Water Interface Studied with Neutron Reflection: Formation of a Condensed Lamellar Phase at the CMC

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Phase pure α-Mn₂O₃ prisms and their bifunctional electrocatalytic activity in oxygen evolution and reduction reactions