Where Is the Most Hydrophobic Region? Benzopurpurine Self-Assembly at the Calcite–Water Interface

Nalbach, Martin; Raiteri, Paolo; Klassen, Stefanie; Schäfer, Sven; Gale, Julian D.; Bechstein, Ralf; Kühnle, Angelika

doi:10.1021/acs.jpcc.7b09825

Cited by 18 publications

(30 citation statements)

References 68 publications

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“…Classical MD simulations were run using LAMMPS . The NPT-equilibrated cell at 300 K and 1 atm was taken from our previous work . Using this cell, we performed a 60 ns NVT simulation, controlling the temperature at 300 K with the velocity–rescaling thermostat of Bussi et al .…”

Section: Methodsmentioning

confidence: 99%

Does the Structural Water within Gypsum Remain Crystalline at the Aqueous Interface?

Söngen

Silvestri

Roshni³

et al. 2021

J. Phys. Chem. C

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Solid−liquid interfaces are omnipresent in nature and technology. Processes occurring at the mineral−water interface are pivotal in geochemistry, biology, as well as in many technological areas. In this context, gypsumthe dihydrate of calcium sulfateplays a prominent role due to its widespread distribution in the Earth's crust and its manifold applications in technology. Despite this, many fundamental questions regarding the molecular-scale structure, including the fate of the crystal water molecules at the aqueous interface, remain poorly studied. Here, we present an atomic force microscopy (AFM) and molecular dynamics (MD) investigation to elucidate molecular-level details of the gypsum−water interface. Three-dimensional AFM data shed light into the hydration structure, revealing one water molecule per surface unit cell area in the lowest layer accessible to experiment. Comparing with simulation data suggests that the AFM tip does not penetrate into the surface-bound layer of crystal water. Instead, the first hydration water layer on top of the crystal water is mapped. Our findings indicate that the crystal water at the interface remains tightly bound, even when in contact with bulk water. Thus, the interfacial chemistry is governed by the crystal water rather than the calcium or sulfate ions.

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Section: Methodsmentioning

confidence: 99%

Does the Structural Water within Gypsum Remain Crystalline at the Aqueous Interface?

Söngen

Silvestri

Roshni³

et al. 2021

J. Phys. Chem. C

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“…The water was modelled with the flexible SPC/FW model 80 . All interactions involving the organics came from the Generalised Amber Force Field (GAFF) 81 and the cross-terms were as described in Nalbach et al 82 . It should be noted that, unlike the CaCO 3 interactions, the organic force fields have not been validated against experimental or ab initio thermodynamic data for these organic molecules.…”

Section: Methodsmentioning

confidence: 99%

“…It should be noted that, unlike the CaCO 3 interactions, the organic force fields have not been validated against experimental or ab initio thermodynamic data for these organic molecules. However, there is precedent for using this particular combination of force fields to model calcite/water/organic systems 82 .…”

Section: Methodsmentioning

confidence: 99%

Hydroxyl-rich macromolecules enable the bio-inspired synthesis of single crystal nanocomposites

et al. 2019

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Acidic macromolecules are traditionally considered key to calcium carbonate biomineralisation and have long been first choice in the bio-inspired synthesis of crystalline materials. Here, we challenge this view and demonstrate that low-charge macromolecules can vastly outperform their acidic counterparts in the synthesis of nanocomposites. Using gold nanoparticles functionalised with low charge, hydroxyl-rich proteins and homopolymers as growth additives, we show that extremely high concentrations of nanoparticles can be incorporated within calcite single crystals, while maintaining the continuity of the lattice and the original rhombohedral morphologies of the crystals. The nanoparticles are perfectly dispersed within the host crystal and at high concentrations are so closely apposed that they exhibit plasmon coupling and induce an unexpected contraction of the crystal lattice. The versatility of this strategy is then demonstrated by extension to alternative host crystals. This simple and scalable occlusion approach opens the door to a novel class of single crystal nanocomposites.

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“…A possible structure for the adsorbed stearic acid layer could be formation of a monolayer of alkyl chains, due to physisorption of the stearic acid by charge interaction of the head group with carbonate surfaces, due to steric effects, and oblique or gauche conformation of the aliphatic hydrocarbon chain, as well as physisorption of the stearic acid molecule head group to the surface by hydrogen bonds [68]. Another possible structure of the adsorbed layer could be physical adsorption of alkyl chains due to alkyl-alkyl interactions (London dispersion force), as dimers (tail-to-tail arrangement), creating the upper layer of surfactant [69]. This arrangement results in the negatively charged head groups of stearic acid molecules being exposed to the aqueous solution leading to more negative surface charges.…”

Section: Effect Of Stearic Acidmentioning

confidence: 99%

Mechanisms of Surface Charge Modification of Carbonates in Aqueous Electrolyte Solutions

Derkani

Fletcher

Fedorov

et al. 2019

Colloids and Interfaces

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The influence of different types of salts (NaCl, CaCl 2 , MgCl 2 , NaHCO 3 , and Na 2 SO 4 ) on the surface characteristics of unconditioned calcite and dolomite particles, and conditioned with stearic acid, was investigated. This study used zeta potential measurements to gain fundamental understanding of physico-chemical mechanisms involved in surface charge modification of carbonate minerals in the presence of diluted salt solutions. By increasing the salt concentration of divalent cationic salt solution (CaCl 2 and MgCl 2 ), the zeta potential of calcite particles was altered, resulting in charge reversal from negative to positive, while dolomite particles maintained positive zeta potential. This is due to the adsorption of potential-determining cations (Ca 2 + and Mg 2 + ), and consequent changes in the structure of the diffuse layer, predominantly driven by coulombic interactions. On the other hand, chemical adsorption of potential-determining anions (HCO 3 - and SO 4 2 - ) maintained the negative zeta potential of carbonate surfaces and increased its magnitude up to 10 mM, before decreasing at higher salt concentrations. Physisorption of stearic acid molecules on the calcite and dolomite surfaces changed the zeta potential to more negative values in all solutions. It is argued that divalent cations (Ca 2 + and Mg 2 + ) would result in positive and neutral complexes with stearic acid molecules, which may result in strongly bound stearic acid films, whereas ions resulting in negative mineral surface charges (SO 4 2 - and HCO 3 - ) will cause stearic acid films to be loosely bound to the carbonate mineral surfaces. The suggested mechanism for surface charge modification of carbonates, in the presence of different ions, is changes in both distribution of ions in the diffuse layer and its structure as a result of ion adsorption to the crystal lattice by having a positive contribution to the disjoining pressures when changing electrolyte concentration. This work extends the current knowledge base for dynamic water injection design by determining the effect of salt concentration on surface electrostatics.

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Where Is the Most Hydrophobic Region? Benzopurpurine Self-Assembly at the Calcite–Water Interface

Cited by 18 publications

References 68 publications

Does the Structural Water within Gypsum Remain Crystalline at the Aqueous Interface?

Does the Structural Water within Gypsum Remain Crystalline at the Aqueous Interface?

Hydroxyl-rich macromolecules enable the bio-inspired synthesis of single crystal nanocomposites

Mechanisms of Surface Charge Modification of Carbonates in Aqueous Electrolyte Solutions

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