Mechanism of wettability alteration of the calcite {101[combining macron]4} surface.

To understand the mechanism of wettability alteration of calcite, a typical mineral in oil reservoirs, the interactions of deionized water and brine (with different compositions) with the calcite {101[combining macron]4} surface are investigated using a combination of molecular dynamics and first-principles simulations. We show that two distinct water adsorption layers are formed through hydrogen bonding and electrostatic interactions with the calcite {101[combining macron]4} surface as well as hydrogen bonding between the water molecules. These highly ordered water layers resist penetration of large stable Mg2+ and Ca2+ hydrates. As Na+ and Cl- hydrates are less stable, Na+ and Cl- ions may penetrate the ordered water layers to interact with the calcite {101[combining macron]4} surface. In contact with this surface, Na+ interacts significantly with water molecules, which increases the water-calcite interaction (wettability of calcite), in contrast to Cl-. We propose that formation of Na+ hydrates plays an important role in the wettability alteration of the calcite {101[combining macron]4} surface.

Selective Electrocatalytic Oxidation of Biomass-Derived 5-Hydroxymethylfurfural to 2,5-Diformylfuran: from Mechanistic Investigations to Catalyst Recovery.

Invited for this month's cover is the group of Gyorgy Szekely at King Abdullah University of Science and Technology (KAUST). The image shows the efficient TEMPO-based electrocatalytic transformation of biomass-based C6 -platform chemical HMF to DFF using non-precious-metal-based electrodes in green solvents with nanofiltration-enabled catalyst recovery. The Full Paper itself is available at 10.1002/cssc.202000453.

Selective Electrocatalytic Oxidation of Biomass-Derived 5-Hydroxymethylfurfural to 2,5-Diformylfuran: from Mechanistic Investigations to Catalyst Recovery.

The catalytic transformation of bio-derived compounds, specifically 5-hydroxymethylfurfural (HMF), into value-added chemicals may provide sustainable alternatives to crude oil and natural gas-based products. HMF can be obtained from fructose and successfully converted to 2,5-diformylfuran (DFF) by an environmentally friendly organic electrosynthesis performed in an ElectraSyn reactor, using cost-effective and sustainable graphite (anode) and stainless-steel (cathode) electrodes in an undivided cell, eliminating the need for conventional precious metal electrodes. In this work, the electrocatalysis of HMF is performed by using green solvents such as acetonitrile, γ-valerolactone, as well as PolarClean, which is used in electrocatalysis for the first time. The reaction parameters and the synergistic effects of the TEMPO catalyst and 2,6-lutidine base are explored both experimentally and through computation modeling. The molecular design and synthesis of a size-enlarged C3 -symmetric tris-TEMPO catalyst are also performed to facilitate a sustainable reaction work-up through nanofiltration. The obtained performance is then compared with those obtained by heterogeneous TEMPO alternatives recovered by using an external magnetic field and microfiltration. Results show that this new method of electrocatalytic oxidation of HMF to DFF can be achieved with excellent selectivity, good yield, and excellent catalyst recovery.

Finely Tuned Submicroporous Thin-Film Molecular Sieve Membranes for Highly Efficient Fluid Separations.

Polymeric membranes with increasingly high permselective performances are gaining a significant role in lowering the energy burden and improving the environmental sustainability of complex chemical separations. However, the commercial deployment of newly designed materials with promising intrinsic properties for fluid separations has been stalled by challenges associated with fabrication and scale up of low-cost, high-performance, defect-free thin-film composite (TFC) membranes. Here, a facile method to fabricate next-generation TFC membranes using a bridged-bicyclic triptycene tetra-acyl chloride (Trip) building block with a large fraction of finely tuned structural submicroporosity (pore size < 4 Å) is demonstrated. The TFCs exhibit superb potential for removal of small (≈200 g mol-1 ) organic microcontaminants from organic solvent streams by showing both improved rejection and permeance in organic systems compared to current state-of-the-art commercial membranes. The TFCs also display unprecedented properties for desalination applications with performance located far above the current water permeance/sodium chloride rejection trendline. The strategy of using highly contorted triptycene building blocks with well-defined interconnected internal free volume elements establishes a scalable, generalized approach to fabricate highly selective, submicroporous TFC membranes for a wide variety of challenging energy-intensive fluid separations.

Defected and Functionalized Germanene-based Nanosensors under Sulfur Comprising Gas Exposure.

Efficient sensing of sulfur containing toxic gases like H2S and SO2 is of the utmost importance due to the adverse effects of these noxious gases. Absence of an efficient 2D-based nanosensor capable of anchoring H2S and SO2 with feasible binding and an apparent variation in electronic properties upon the exposure of gas molecules has motivated us to explore the promise of a germanene nanosheet (Ge-NS) for this purpose. In the present study, we have performed a comprehensive computational investigation by means of DFT-based first-principles calculations to envisage the structural, electronic, and gas sensing properties of pristine, defected, and metal substituted Ge-NSs. Our initial screening has revealed that although interaction of SO2 with pristine Ge-NSs is within the desirable range, H2S binding however falls below the required values to guarantee an effective sensing. To improve the binding characteristics, we have considered the interactions between H2S and SO2 with defected and metal substituted Ge-NS. The systematic removals of Ge atoms from a reasonably large super cell lead to monovacancy, divacancies, and trivacancies in Ge-NS. Similarly, different transition metals like As, Co, Cu, Fe, Ga, Ge, Ni, and Zn have been substituted into the monolayer to realize substituted Ge-NS. Our van der Waals corrected DFT calculations have concluded that the vacancy and substitution defects not only improve the binding characteristics but also enhance the sensing propensity of both H2S and SO2. The total and projected density of states show significant variations in electronic properties of pristine and defected Ge-NSs before and after the exposure to the gases, which are essential in constituting a signal to be detected by the external circuit of the sensor. We strongly believe that our present work would not only advance the knowledge towards the application of Ge-NS-based sensing but also provide motivation for the synthesis of such efficient nanosensor for H2S and SO2 based on Ge monolayer.

Controlling the orientation of nucleobases by dipole moment interaction with graphene/h-BN interfaces.

The interfaces in 2D hybrids of graphene and h-BN provide interesting possibilities of adsorbing and manipulating atomic and molecular entities. In this paper, with the aid of density functional theory, we demonstrate the adsorption characteristics of DNA nucleobases at different interfaces of 2D hybrid nanoflakes of graphene and h-BN. The interfaces provide stronger binding to the nucleobases in comparison to pure graphene and h-BN nanoflakes. It is also revealed that the individual dipole moments of the nucleobases and nanoflakes dictate the orientation of the nucleobases at the interfaces of the hybrid structures. The results of our study point towards a possible route to selectively control the orientation of individual molecules in biosensors.

Spectroscopic and DFT studies on 6-aminophenanthridine and its derivatives provide insights in their activity towards ribosomal RNA.

6-Aminophenanthridine (6AP), a plant alkaloid possessing antiprion activity, inhibits ribosomal RNA dependent protein folding activity of the ribosome (referred as PFAR). We have compared 6AP and its three derivatives 6AP8Cl, 6AP8CF3 and 6APi for their activity in inhibition of PFAR. Since PFAR inhibition requires 6AP and its derivatives to bind to the ribosomal RNA (rRNA), we have measured the binding affinity of these molecules to domain V of 23S rRNA using fluorescence spectroscopy. Our results show that similar to the antiprion activity, both the inhibition of PFAR and the affinity towards rRNA follow the order 6AP8CF3 > 6AP8Cl > 6AP, while 6APi is totally inactive. To have a molecular insight for the difference in activity despite similarities in structure, we have calculated the nucleus independent chemical shift using first principles density functional theory. The result suggests that the deviation of planarity in 6APi and steric hindrance from its bulky side chain are the probable reasons which prevent it from interacting with rRNA. Finally, we suggest a probable mode of action of 6AP, 6AP8CF3 and 6AP8Cl towards rRNA.