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1. Controllable membrane remodeling by a modified fragment of the apoptotic protein Bax

   https://doi.org/10.1039/D0FD00070A  

   Schaefer, Katherine G. ; Grau, Brayan ; Moore, Nicolas ; Mingarro, Ismael ; King, Gavin ; Barrera, Francisco ( January 2020 , Faraday Discussions)

   null (Ed.)

   Intrinsic apoptosis is orchestrated by a group of proteins that mediate the coordinated disruption of mitochondrial membranes. Bax is a multi-domain protein that, upon activation, disrupts the integrity of the mitochondrial outer membrane by forming pores. We strategically introduced glutamic acids into a short sequence of the Bax protein that constitutively creates membrane pores. The resulting BaxE5 peptide efficiently permeabilizes membranes at acidic pH, showing low permeabilization at neutral pH. Atomic force microscopy (AFM) imaging showed that at acidic pH BaxE5 established several membrane remodeling modalities that progressively disturbed the integrity of the lipid bilayer. The AFM data offers vistas on the membrane disruption process, which starts with pore formation and progresses through localized exposure of membrane monolayers leading to stable and thin (16 Å) lipid-peptide complexes. The different types of membrane morphology observed in the presence of BaxE5 suggest that the peptide can establish different types of membrane interaction. BaxE5 adopts a rare unstructured conformation when bound to membranes, which might facilitate the dynamic transition between those different states, and then promote membrane digestion. 

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2. Magic-angle spinning NMR spectroscopy provides insight into the impact of small molecule uptake by G-quartet hydrogels

   https://doi.org/10.1039/D0MA00475H  

   Manjunatha Reddy, G. N. ; Peters, Gretchen ; Tatman, Ben ; Rajan, Teena S. ; Kock, Si Min ; Zhang, Jing ; Frenguelli, Bruno G. ; Davis, Jeffery ; Marsh, Andrew ; Brown, Steven P. ( January 2020 , Materials Advances)

   Small molecule guests influence the functional properties of supramolecular hydrogels. Molecular-level understanding of such sol-gel compositions and structures is challenging due to the lack of long-range order and inherently heterogeneous sol-gel interface. In this study, insight into the uptake process of biologically relevant small molecules into guanosine-quartet(G4) borate hydrogels is obtained by gel-state magic-angle spinning (MAS) NMR spectroscopy. G4∙K + borate hydrogel can absorb up to 0.3 equivalent of cationic methylene blue (MB) without a significant disruption of the G4 fibrils that make up the gel, whereas the addition of over 0.3 equivalents of MB to the same gel leads to a gel-to-sol transition. The gel-to-sol transition process is characterized ex situ by analyzing and comparing the 1 H and 11 B MAS NMR spectra acquired before and after the MB uptake. In particular, 11 B isotropic chemical shifts and quadrupole interactions were determined by analyzing the 11 B MAS NMR spectra acquired at different magnetic fields, 11.7 T, 14.1 T and 20 T, which enable the different local bonding environments of borate anions in sol- and gel domains to be distinguished and identified. By comparison, uptake of heterocyclic molecules such as adenine, cytosine and 1-methylthymine into G4∙Na + borate hydrogels lead to stiff and clear gels while increasing the solubility of the nucleobases as compared to the solubility of the same compounds in water. G4∙Na + gel can uptake one equiv. of adenine with minimal disruption to the sol-gel framework, thus enhancing the adenine solubility up to an order of magnitude as compared to water. Combined multinuclear ( 1 H, 11 B and 23 Na) NMR spectroscopy analysis and vial inversion tests revealed that the nucleobases are embedded into pores of the sol phase rather than being closely interacting with the G-4 fibrils that make up the gel phase. These results indicate that G-4 hydrogels have potential applications as carrier systems for small molecules. Gel-state MAS NMR spectroscopy can be used to gain insight into host-guest interactions in complex heterogeneous sol-gel systems, which is often difficult to obtain from the conventional techniques such as X-ray scattering, electron microscopy and optical spectroscopy. 

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3. Revealing the Sodium Storage Mechanisms in Hard Carbon Pores

   https://doi.org/10.1002/aenm.202302171  

   Kitsu Iglesias, Luis ; Antonio, Emma N. ; Martinez, Tristan D. ; Zhang, Liang ; Zhuo, Zengqing ; Weigand, Steven J. ; Guo, Jinghua ; Toney, Michael F. ( October 2023 , Advanced Energy Materials)

   Hard carbon (HC) is the most promising anode for the commercialization of sodium‐ion batteries (NIBs); however, a general mechanism for sodium storage in HC remains unclear, obstructing the development of highly efficient anodes for NIBs. To elucidate the mechanism of sodium storage in the pores, operando synchrotron small‐angle X‐ray scattering, wide‐angle X‐ray scattering, X‐ray absorption near edge structure, Raman spectroscopy, and galvanostatic measurements are combined. The multimodal approach provides mechanistic insights into the sodium pore‐filling process for different HC microstructures including the pore sizes that are preferentially filled, the extent to which different pore sizes are filled, and how the defect concentration influences pore filling. It is observed that sodium in the larger pores has an increased pseudo‐metallic sodium character consistent with larger sodium clusters. Furthermore, it is shown that the HCs prepared at higher pyrolysis temperatures have a larger capacity from sodium stored in the pores and that sodium intercalation between graphene layers occurs simultaneously with the pore filling in the plateau region. Opportunities are outlined to improve the performance of HC anodes by fully utilizing the pores for sodium storage, helping to pave the way for the commercialization of sodium ion batteries.

    

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4. Pore‐scale Study of Ion Transport Mechanisms in Inhomogeneously Charged Nanoporous Rocks: Impacts of Interface Properties on Macroscopic Transport

   https://doi.org/10.1029/2018JB017200  

   Alizadeh, Amer ; Jin, Xu ; Wang, Moran ( June 2019 , Journal of Geophysical Research: Solid Earth)

   The electrokinetic transport mechanisms of multispecies ions through 3‐D nanoporous rocks with chemical reaction at the solid‐aqueous solution interfaces are investigated. We systematically study the multiphysics transport phenomena by considering either inhomogeneous (local surface charge based on local pH and ion concentrations) or prescribed homogeneous surface charge at solid‐aqueous solution interface while the pores are screened via electric double layers. We develop a lattice Boltzmann numerical framework to solve the set of governing equations (Poisson‐Nernst‐Planck plus Navier–Stokes). Our modeling results reveal that the averaged local electric potential of the nanoporous rock is significantly underestimated (about 83%) when a homogeneous surface charge is prescribed based on the bulk solution properties. It is shown that increasing the porosity of the nanoporous media considerably increases the absolute values and inhomogeneity of the surface charge, which means that while the electric double layers screened the pores, increasing the porosity enhances the ion selectivity of the porous medium. When the scenario with inhomogeneous charge is taken into account, the predicted electroosmotic permeability and tortuosity are higher in comparison with the prescribed homogeneous case. Moreover, we have studied the electrostatic tortuosity, coupling coefficient, and the effective excess charge density of the nanoporous rocks. The results demonstrate that ignoring the inhomogeneity of surface charges may cause erroneous prediction of the ion transport through porous rocks with chemically active surfaces.

    

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5. All-dry free radical polymerization inside nanopores: Ion-milling-enabled coating thickness profiling revealed “necking” phenomena

   https://doi.org/10.1116/6.0001718  

   Cheng, Yifan ; Khlyustova, Alexandra ; Yang, Rong ( May 2022 , Journal of Vacuum Science & Technology A)

   Conformal coating of nanopores with functional polymer nanolayers is the key to many emerging technologies such as miniature sensors and membranes for advanced molecular separations. While the polymer coatings are often used to introduce functional moieties, their controlled growth under nanoconfinement could serve as a new approach to manipulate the size and shape of coated nanopores, hence, enabling novel functions like molecular separation. However, precise control of coating thickness in the longitudinal direction of a nanopore is limited by the lack of a characterization method to profile coating thickness within the nanoconfined space. Here, we report an experimental approach that combines ion milling (IM) and high-resolution field emission scanning electron microscopy (FESEM) for acquiring an accurate depth profile of ultrathin (∼20 nm or less) coatings synthesized inside nanopores via initiated chemical vapor deposition (iCVD). The enhanced capability of this approach stems from the excellent x–y resolution achieved by FESEM (i.e., 4.9 nm/pixel), robust depth ( z) control enabled by IM (step size as small as 100 nm with R² = 0.992), and the statistical power afforded by high-throughput sampling (i.e., ∼2000 individual pores). With that capability, we were able to determine with unparalleled accuracy and precision the depth profile of coating thickness and iCVD kinetics along 110-nm-diameter nanopores. That allowed us to uncover an unexpected coating depth profile featuring a maximum rate of polymerization at ∼250 nm underneath the top surface, i.e., down the pores, which we termed “necking.” The necking phenomenon deviates considerably from the conventionally assumed monotonous decrease in thickness along the longitudinal direction into a nanopore, as predicted by the diffusion-limited kinetics model of free radical polymerization. An initiator-centric collision model was then developed, which suggests that under the experimental conditions, the confinement imposed by the nanopores may lead to local amplification of the effective free radical concentration at z ≤ 100 nm and attenuation at z ≥ 500 nm, thus contributing to the observed necking phenomenon. The ion-milling-enabled depth profiling of ultrathin coatings inside nanopores, along with the initiator-mediated coating thickness control in the z-direction, may serve to enhance the performance of size-exclusion filtration membranes and even provide more flexible control of nanopore shape in the z dimension.

    

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