| 1. |
- Beal, Jacob, et al.
(author)
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Robust estimation of bacterial cell count from optical density
- 2020
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In: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Journal article (peer-reviewed)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 2. |
- Fu, Yao, et al.
(author)
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Duet of Acetate and Water at the Defects of Metal-Organic Frameworks
- 2019
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In: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 19:3, s. 1618-1624
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Journal article (peer-reviewed)abstract
- Metal-organic frameworks (MOFs) are porous crystalline materials with promising applications in molecular adsorption, separation, and catalysis. It has been discovered recently that structural defects introduced unintentionally or by design could have a significant impact on their properties. However, the exact chemical composition and structural evolution under different conditions at the defects are still under debate. In this study, we performed multidimensional solid-state nuclear magnetic resonance (SSNMR) coupled with computer simulations to elucidate an important scenario of MOF defects, uncovering the dynamic interplay between residual acetate and water. Acetate, as a defect modulator, and water, as a byproduct, are prevalent defect-associated species, which are among the key factors determining the reactivity and stability of defects. We discovered that acetate molecules coordinate to a single metal site monodentately and pair with water at the neighboring position. The acetates are highly flexible, which undergo fast libration as well as a slow kinetic exchange with water through dynamic hydrogen bonds. The dynamic processes under variable temperatures and different hydration levels have been quantitatively analyzed across a broad time scale from microseconds to seconds. The integration of SSNMR and computer simulations allows a precision probe into defective MOF structures with intrinsic dynamics and disorder.
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| 3. |
- Kang, Zhengzhong, 1990-, et al.
(author)
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Adsorption and folding of single strand DNA on metal-organic frameworks: a molecular simulation study
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Other publication (other academic/artistic)abstract
- DNA-MOF nanoparticles based on the loading, release, and conformational change of DNA on MOFs have been frequently explored in gene therapy, drug delivery, and biosensor design. Nevertheless, the mechanism of DNA-MOF interactions, which is a fundamental issue behind these applications, remains largely unclear. Here, we applied molecular simulation methods to study systematically the adsorption and folding of ssDNA with different sequences on ideal and defective UiO-66-NH2 MOFs. We find that the ssDNA prefers to be adsorbed on the surfaces rather than inside the cages due to the size limitation of the cages. It is difficult for the ssDNA to be adsorbed on the ideal MOF surface through van der Waals interactions but it can be stably loaded on the defective MOF surface through electrostatic interactions. The whole process of the ssDNA adsorption onto the defective MOFs includes three stages: fast adsorption, conformational reconfiguration, and lock-down adsorption. The loading state of the ssDNA on UiO-66-NH2 is the coexistence of the adsorbed and dangling nucleotides. The binding of the ssDNA on the MOFs is dominated by the multiple point anchoring of the phosphate groups of the ssDNA on the clusters of UiO-66-NH2. Water layers with complex hydrogen-bond network function as a gate, preventing the ssDNA from approaching to UiO-66-NH2 before adsorption and inhibiting it from leaving UiO-66-NH2 after anchoring. Unlike the circular folding structure in the solution, the adsorbed ssDNA displays a slender conformation or duplex like structure. Our results thus provide a deep understanding of DNA-MOF interactions.
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| 4. |
- Sun, Xuan, et al.
(author)
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Construction of Electron Transfer Network by Self-Assembly of Self-n-Doped Fullerene Ammonium Iodide
- 2016
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 28:23, s. 8726-8731
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Journal article (peer-reviewed)abstract
- Construction of pi-conjugation network in ordered fullerenes by self-assembly remains challenging for improving their optoelectronic performance and developing advanced materials. Here, we present a layered stacking of self-n-doped fullerene ammonium iodide (PCBANI) through a delicate balance among iodide anion-C-60 pi, electrostatic, and C-60 pi-pi interactions to construct an unprecedented supra molecular system. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and computational modeling are carried out to clarify the structure. Remarkably, the formation of intermolecular iodide anion pi interactions between iodide and the surrounded fullerene cores yields an iodide-linked C-60 pi-pi two-dimensional (2-D) network. Consequently, the ordered and tightly packed fullerenes sandwiching iodide could facilitate electron transfer along the network system. Comparative devices incorporating the disordered films show dramatically decreased current densities and manifest the importance of the pi-extended network for electron transfer. This work provides a key strategy to control the packing of ordered electron-transport materials to suppress defect formation. Moreover, engineering self-assembly of self-n-doped fullerenes with novel architectures, such as nanowire, nanotube, and nanoparticle would yield new functionalities that are suitable for photovoltaic devices, nanoelectronics, etc.
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