Enantiomeric excess of chiral compounds is a key parameter that determines their activity or therapeutic action. The current paradigm for rapid measurement of enantiomeric excess using NMR is based on the formation of diastereomeric complexes between the chiral analyte and a chiral resolving agent, leading to (at least) two species with no symmetry relationship. Here we report an effective method of enantiomeric excess determination using a symmetrical achiral molecule as the resolving agent, which is based on the complexation with analyte (in the fast exchange regime) without the formation of diastereomers. The use of N,N′-disubstituted oxoporphyrinogen as the resolving agent makes this novel method extremely versatile, and appropriate for various chiral analytes including carboxylic acids, esters, alcohols and protected amino acids using the same achiral molecule. The model of sensing mechanism exhibits a fundamental linear response between enantiomeric excess and the observed magnitude of induced chemical shift non-equivalence in the 1H NMR spectra.

The bacterium Shewanella oneidensis has evolved a sophisticated electron transfer (ET) machinery to export electrons from the cytosol to extracellular space during extracellular respiration. At the heart of this process are decaheme proteins of the Mtr pathway, MtrC and MtrF, located at the external face of the outer bacterial membrane. Crystal structures have revealed that these proteins bind 10 c-type hemes arranged in the peculiar shape of a staggered cross that trifurcates the electron flow, presumably to reduce extracellular substrates while directing electrons to neighboring multiheme cytochromes at either side along the membrane. Especially intriguing is the design of the heme junctions trifurcating the electron flow: they are made of coplanar and T-shaped heme pair motifs with relatively large and seemingly unfavorable tunneling distances. Here, we use electronic structure calculations and molecular simulations to show that the side chains of the heme rings, in particular the cysteine linkages inserting in the space between coplanar and T-shaped heme pairs, strongly enhance electronic coupling in these two motifs. This results in an ≈103-fold speedup of ET steps at heme junctions that would otherwise be rate limiting. The predicted maximum electron flux through the solvated proteins is remarkably similar for all possible flow directions, suggesting that MtrC and MtrF shuttle electrons with similar efficiency and reversibly in directions parallel and orthogonal to the outer membrane. No major differences in the ET properties of MtrC and MtrF are found, implying that the different expression levels of the two proteins during extracellular respiration are not related to redox function.

We study solvent-free electron transport across two multi-heme cytochrome c-type proteins, MtrF and STC, and find that they are better at conducting than non- or mono heme proteins.

To get insight of the formation mechanism of solid electrolyte interphase (SEI) film in Lithium-ion battery (LIB), we examine a probable scenario, referred to as "surface growth mechanism," for electrolyte involving ethylene carbonate (EC) solvent and vinylene carbonate (VC) additive by using density functional theory (DFT). We first extracted stable SEI film components (SFCs) for the EC/VC electrolyte and constructed probable SFC aggregates via DFT molecular dynamics. We then examined their solubility in the EC solution, their adhesion to a model graphite electrode, and the electronic properties. The results showed that the SFC aggregates are characterized by "unstable adhesion" to the graphite surface and "high electronic insulation" against the EC solution. These characteristics preclude explaining SEI growth up to a typical thickness of several tens of nanometers based on the surface growth mechanism. With the present results, we propose "near-shore aggregation" mechanism, where the SFCs formed at the electrode surface desorb into the near-shore region and form aggregates. The SFC aggregates coalesce and come into contact with the electrode to complete the SEI formation. The present model provides a novel perspective for the long-standing problem of SEI formation. Lithium-ion batteries (LIBs) have attracted considerable attention for use in larger power sources like electric vehicles and energy storage system because of their high energy densities.1,2 For such use, a higher degree of safety, a longer cycle life, higher voltage and capacity will be indispensable in the future. An important key of the stability and durability of the LIB is the solid electrolyte interphase (SEI) formed at the negative electrode-electrolyte interface.3,4 It is generally accepted that molecules in the electrolyte solution reductively decompose to form various SEI film components (SFCs), such as organic oligomers (e.g., (CH 2 OCO 2 Li) 2 , and ROCO 2 Li) and inorganic moieties (e.g., Li 2 CO 3 , LiF) at the first charging, 5 and that the SFCs precipitate on the electrode surface to form a stable SEI film with a thickness of several tens of nanometers. 6 The SEI hinders electron transport from the electrode to the electrolyte solution, preventing further electrolyte decomposition, while allowing Li + ion transport. This property decreases the irreversible capacity and improves the safety of LIBs. Additives to the electrolyte solution also have a large impact on SEI performance. Even a small amount of additive up to a few wt% significantly improves the irreversible capacity and cyclability.7 In general, the additive molecules modify the SFCs and lead to different properties of the SEI film. Despite the important roles of the SEI in LIB operation, the microscopic formation processes are still unclear because of the difficulty in operando observations of chemical reactions at the electrodeelectrolyte interfaces.The detailed formation processes of SEI have been typically assumed to involve "surface growth mechanism", mainly in the firs...

Multi-heme proteins have attracted much attention recently due to their prominent role in mediating extracellular electron transport (ET), but one of their key fundamental properties, the rate constants for ET between the constituent heme groups, have so far evaded experimental determination. Here we report the set of heme-heme theoretical ET rate constants that define electron flow in the tetra-heme protein STC by combining a novel projector-operator diabatization approach for electronic coupling calculation with molecular dynamics simulation of ET free energies. On the basis of our calculations, we find that the protein limited electron flux through STC in the thermodynamic downhill direction (heme 1→4) is ∼3 × 10 s. We find that cysteine linkages inserting in the space between the two terminal heme pairs 1-2 and 3-4 significantly enhance the overall electron flow, by a factor of about 37, due to weak mixing of the sulfur 3p orbital with the Fe-heme d orbitals. While the packing density model, and to a higher degree, the pathway model of biological ET partly capture the predicted rate enhancements, our study highlights the importance of the atomistic and chemical nature of the tunneling medium at short biological tunneling distances. Cysteine linkages are likely to enhance electron flow also in the larger deca-heme proteins MtrC and MtrF, where heme-heme motifs with sub-optimal edge-to-edge distances are used to shuttle electrons in multiple directions.

Building on our previous work (J. Phys. Chem. C, 2016, 120, 16561), using an empirical model we run both classical and path-integral molecular dynamics simulations for a type II clathrate hydrate containing different amounts of guest H molecules from 1 to 5 molecules per large cage, with results presented at temperatures of 50, 100 K and 200 K. We present results for the density isosurfaces of the guest molecules at all different occupations and temperatures, showing how the density approaches the perfect tetrahedral structure which has been found for the n = 4 case in which each molecule sits on the vertex of a tetrahedron about the centre of each large cage. We calculate free-energy profiles of the molecules over the volume interior to the cage, and using umbrella sampling, we also calculate the free energy barrier for the molecule to hop between cages. We show that this barrier reduces almost linearly for n = 1-3 molecules per large cage, but becomes larger than would be expected (from extrapolation) for the n = 4 case, with this departure from linearity becoming larger at lower temperatures. We show that, perhaps counter-intuitively, these barriers tend to increase with raising the temperature, and also counter-intuitively that quantisation of the nuclei acts to increase the barriers. Finally, for the n = 4 case, a comparison is made between the empirical model results and those from an ab initio molecular dynamics calculation, which shows that qualitative agreement exists between the two models.

Multi-heme cytochromes (MHCs) are fascinating proteins used by bacterial organisms to shuttle electrons within, between, and out of their cells. When placed in solid-state electronic junctions, MHCs support temperature-independent currents over several nanometers that are 3 orders of magnitude higher compared to other redox proteins of similar size. To gain molecular-level insight into their astonishingly high conductivities, we combine experimental photoemission spectroscopy with DFT+Σ current–voltage calculations on a representative Gold-MHC-Gold junction. We find that conduction across the dry, 3 nm long protein occurs via off-resonant coherent tunneling, mediated by a large number of protein valence-band orbitals that are strongly delocalized over heme and protein residues. This picture is profoundly different from the electron hopping mechanism induced electrochemically or photochemically under aqueous conditions. Our results imply that the current output in solid-state junctions can be even further increased in resonance, for example, by applying a gate voltage, thus allowing a quantum jump for next-generation bionanoelectronic devices.

We have investigated the effects of external static electric fields applied to a wide variety of TiO2/water interfaces using nonequilibrium molecular-dynamics techniques. The externally applied electric fields were found to be relatively weak vis-à-vis intrinsic electric fields computed in the interfacial regions, the magnitude of which varied from 1.8 V/Å toward bulklike water up to 4.5 V/Å at the interface. The molecular arrangement of the first hydration layer is determined fully by the surface structure of TiO2, where water is coordinated to unsaturated titanium atoms and/or interacting with exposed surface oxygen atoms. Moreover, the water dipoles tend to align with the strong intrinsic field. As a result, diffusion of water in this region was found to be by 1 order of magnitude lower than that of bulk water; application of an external electric field did not lead to a considerable change. In contrast to unperturbed diffusivity, a rather strong response of hydrogen-bond lifetime to the applied field was observed. The interfacial water is heavily confined, although the extent to which shows marked variation with specific surfaces; indeed, this environmental interplay has considerable effect on corresponding IR spectra in the interfacial-water region, and is affected by applied static fields.