Three-dimensional microfiber devices that mimic physiological environments to probe cell mechanics and signaling

Many physiological systems are regulated by cells that alter their behavior in response to changes in their biochemical and mechanical environment. These cells experience this dynamic environment through an endogenous biomaterial matrix that transmits mechanical force and permits chemical exchange with the surrounding tissue. As a result, in vitro systems that mimic three-dimensional, in vivo cellular environments can enable experiments that reveal the nuanced interplay between biomechanics and physiology. Here we report the development of a minimal-profile, three-dimensional (MP3D) experimental microdevice that confines cells to a single focal plane, while allowing the precise application of mechanical displacement to cells and concomitant access to the cell membrane for perfusion with biochemical agonists. The MP3D device--an ordered microfiber scaffold erected on glass--provides a cellular environment that induces physiological cell morphologies. Small manipulations of the scaffold's microfibers allow attached cells to be mechanically probed. Due to the scaffold's minimal height profile, MP3D devices confine cells to a single focal plane, facilitating observation with conventional epifluorescent microscopy. When examining fibroblasts within MP3D devices, we observed robust cellular calcium responses to both a chemical stimulus as well as mechanical displacement of the cell membrane. The observed response differed significantly from previously reported, mechanically-induced calcium responses in the same cell type. Our findings demonstrate a key link between environment, cell morphology, mechanics, and intracellular signal transduction. We anticipate that this device will broadly impact research in fields including biomaterials, tissue engineering, and biophysics.     

RGB‐Color Intensiometric Indicators to Visualize Spatiotemporal Dynamics of ATP in Single Cells

Adenosine triphosphate (ATP) provides energy for the regulation of multiple cellular processes in living organisms. Capturing the spatiotemporal dynamics of ATP in single cells is fundamental to our understanding of the mechanisms underlying cellular energy metabolism. However, it has remained challenging to visualize the dynamics of ATP in and between distinct intracellular organelles and its interplay with other signaling molecules. Using single fluorescent proteins, multicolor ATP indicators were developed, enabling the simultaneous visualization of subcellular ATP dynamics in the cytoplasm and mitochondria of cells derived from mammals, plants, and worms. Furthermore, in combination with additional fluorescent indicators, the dynamic interplay of ATP, cAMP, and Ca²⁺ could be visualized in activated brown adipocyte. This set of indicator tools will facilitate future research into energy metabolism.     

C-H-pi interactions in 1-n-butyl-3-methylimidazolium tetraphenylborate molten salt: solid and solution structures

The crystal structure of 1-n-butyl-3-methylimidazolium tetraphenylborate molten salt (1) shows C-H-pi interactions between the hydrogens of the imidazolium cation and the phenyl rings of the tetraphenylborate anion. The imidazolium ring is surrounded by three tetraphenylborate anions that are connected with the same cation by C-H-pi (phenyl rings) interactions. The nearest inter-ion interaction is found between the N-CH-N proton of the cation and the B-phenyl centroid (2.349 A) with a nearly T-shaped geometry. The inter-ionic solution structure of 1 has been investigated by the detection of inter-ionic contacts in 1H NOESY NMR spectra between the protons of the cation and the anion. The 1H-NMR spectra of molten salt 1 is almost independent of its concentration in [D6]DMSO solution, the imidazolium proton chemical shifts are in the expected region and there are no observable NOE effects between the protons of the cation with those of the anion, indicating that 1 behaves in [D6]DMSO as a solvent-separated ion pair. In CDCl3 the 1H-NMR spectra of 1 are concentration dependent and all the imidazolium protons are shielded as compared with those observed in [D6]DMSO. Moreover, the 1H NOESY NMR spectra show all the peaks affected by the interaction between the protons of the imidazolium cation and those of the anion, indicating that in CDCl3 1 possesses a contact ion pair structure. The NCHN proton of the cation exhibits the greatest shielding (up to -4.5 ppm). an indication of the existence of C-H-pi interactions, even in solution. The calculated distance of this proton to the phenyl centroid is 2.3 A for a C-H -pi angle of 180 degrees. The apparent volumes for the cation and anion, calculated from the measured 13C-NMR relaxation times, increase from 38 and 140 A3 in [D6]DMSO to 360 and 600 A3 in CDCl3, respectively; this indicates the formation of floating aggregates of the type (1)(n) in CDCl3 via weak hydrogen bonds, with increasing concentration.     

Surface Termination on Unstable Methylammonium-based Perovskite Using a Steric Barrier for Improved Perovskite Solar Cells

Compared to widely adopted low-dimensional/three-dimensional (LD/3D) heterostructure, functional organic cation based surface termination on perovskite can not only realize advantage of defect passivation but also prevent potential disadvantage of the heterostructure induced intercalation into 3D perovskite. However, it is still very challenging to controllably construct surface termination on organic–inorganic hybrid perovskite because the functional organic cations’ substitution reaction is easy to form LD/3D heterostructure. Here, we report using a novel benzyltrimethylammonium (BTA) functional cation with rational designed steric hindrance to effectively surface terminate onto methylammonium lead triiodide (MAPbI₃) perovskite, which is composed of the most unstable MA cations. The BTA cation is difficult to form a specific 1.5-dimensional perovskite of BTA₄Pb₃I₁₀ by cation substitution with MA cation, which then provides a wide processing window (around 10 minutes) for surface terminating on MAPbI₃ films. Moreover, the BTAI surface terminated BTAI-MAPbI₃ shows better passivation effect than BTA₄Pb₃I₁₀-MAPbI₃ heterojunction. Finally, BTAI surface terminated solar cell (0.085 cm²) and mini-module (11.52 cm²) obtained the efficiencies of 22.03 % and 18.57 %, which are among the highest efficiencies for MAPbI₃ based ones.     

Illuminating Molecular Processes in Living Cells

Lately, scientists have explored approaches to developing fluorescent and/or bioluminescent indicators to pinpoint cellular processes in single living cells. These analytical methods have become a key technology for visualizing and detecting what was otherwise unseen in live cells. The target signaling included second messengers, protein phosphorylations, protein–protein interactions, and protein localizations.     

Steric Mixed‐Cation 2D Perovskite as a Methylammonium Locker to Stabilize MAPbI3

The reduced dimension perovskite including 2D perovskites are one of the most promising strategies to stabilize lead halide perovskite. A mixed‐cation 2D perovskite based on a steric phenyltrimethylammonium (PTA) cation is presented. The PTA‐MA mixed‐cation 2D perovskite of PTAMAPbI₄ can be formed on the surface of MAPbI₃ (PTAI‐MAPbI₃) by controllable PTAI intercalation by either spin coating or soaking. The PTAMAPbI₄ capping layer can not only passivate PTAI‐MAPbI₃ perovskite but also act as MA⁺ locker to inhibit MAI extraction and significantly enhance the stability. The highly stable PTAI‐MAPbI₃ based perovskite solar cells exhibit a reproducible photovoltaic performance with a champion PCE of 21.16 %. Such unencapsulated devices retain 93 % of initial efficiency after 500 h continuous illumination. This steric mixed‐cation 2D perovskite as MA⁺ locker to stabilize the MAPbI₃ is a promising strategy to design stable and high‐performance hybrid lead halide perovskites.     

Seeing what was unseen: new analytical methods for molecular imaging

For nondestructive analysis of chemical processes in living cells, we developed novel intracellular fluorescent indicators for second messengers, protein phosphorylation, and protein/protein interactions that work in single living cells. Key molecules and steps of cellular signaling pathways were visualized under a confocal laser microscope in target live cells using developed fluorescent indicators. A second new approach to molecular imaging is also described. When chemically modified tips were used for STM measurements, contrast enhancements at specific regions in the STM images occurred on the basis of hydrogen bond and metal-coordination interactions. This enabled us to detect not only the distribution of specific chemical species and functional groups but also the orientation of functional groups. The contrast enhancements reflect the increase in a tunneling current due to the overlap of electronic wave functions induced by the chemical interactions between tip and sample.     

Long-Term Stability Analysis of 3D and 2D/3D Hybrid Perovskite Solar Cells Using Electrochemical Impedance Spectroscopy

Despite the remarkable progress in perovskite solar cells (PSCs), their instability and rapid degradation over time still restrict their commercialization. A 2D capping layer has been proved to overcome the stability issues; however, an in-depth understanding of the complex degradation processes over a prolonged time at PSC interfaces is crucial for improving their stability. In the current work, we investigated the stability of a triple cation 3D ([(FA_0.83MA_0.17)Cs_0.05]Pb(I_0.83Br_0.17)₃) and 2D/3D PSC fabricated by a layer-by-layer deposition technique (PEAI-based 2D layer over triple cation 3D perovskite) using a state-of-art characterization technique: electrochemical impedance spectroscopy (EIS). A long-term stability test over 24 months was performed on the 3D and 2D/3D PSCs with an initial PCE of 18.87% and 20.21%, respectively, to suggest a more practical scenario. The current-voltage (J-V) and EIS results showed degradation in both the solar cell types; however, a slower degradation rate was observed in 2D/3D PSCs. Finally, the quantitative analysis of the key EIS parameters affected by the degradation in 3D and 2D/3D PSCs were discussed.     

Conductance Switch of a Bromoplumbate Bistable Semiconductor by Electron‐Transfer Thermochromism

Electron‐transfer (redox) thermochromism was successfully used for switching the conductance of semiconductors, by introducing a thermally active organic component into an inorganic semiconducting framework. A moisture‐resistant semiconductor {(MV)₂[Pb₇Br₁₈]}_n (MV²⁺=methyl viologen cation) has been prepared through an in situ synthetic method for MV²⁺. It features a rare 3D haloplumbate open framework and unprecedented electron‐transfer thermochromic behavior in haloplumbates. The electrical conductivity of this compound dropped significantly after coloration and restored after decoloration, which was satisfactorily explained by valence band XPS and theoretical data. This work not only offers a new approach to modify electrical properties of semiconductors without altering components or structures, but may lead to the development of over‐temperature color indicators, circuit overload protectors or photovoltaic materials.     

蛋白质组学中磷酸化肽的常用富集方法

磷酸化作用是最重要的蛋白质翻译后修饰方式之一,它是蛋白质组学的一个重要分支,在细胞识别、细胞信息传递、基因表达和新陈代谢等方面发挥着重要作用。采用适当方法对磷酸化肽进行分析有助于我们更好地了解生理病理机制。但是直接进行质谱分析时磷酸化肽的信号强度会受到无机盐以及大量非磷酸化肽的抑制,选择性差。为解决这一难题,在质谱分析前要对磷酸化肽进行选择性富集。本文回顾了几种常用的磷酸化肽富集方法,介绍了每种方法的发展状况和常用材料,其中包括固定金属离子亲和色谱法、金属氧化物富集法、强阴阳离子交换色谱法和MALDI靶板富集法。最后总结了各种富集方法的优缺点,对有效的磷酸化肽富集策略进行了前景展望。     

Non-invasive tools for measuring metabolism and biophysical analyte transport: self-referencing physiological sensing

Biophysical phenomena related to cellular biochemistry and transport are spatially and temporally dynamic, and are directly involved in the regulation of physiology at the sub-cellular to tissue spatial scale. Real time monitoring of transmembrane transport provides information about the physiology and viability of cells, tissues, and organisms. Combining information learned from real time transport studies with genomics and proteomics allows us to better understand the functional and mechanistic aspects of cellular and sub-cellular systems. To accomplish this, ultrasensitive sensing technologies are required to probe this functional realm of biological systems with high temporal and spatial resolution. In addition to ongoing research aimed at developing new and enhanced sensors (e.g., increased sensitivity, enhanced analyte selectivity, reduced response time, and novel microfabrication approaches), work over the last few decades has advanced sensor utility through new sensing modalities that extend and enhance the data recorded by sensors. A microsensor technique based on phase sensitive detection of real time biophysical transport is reviewed here. The self-referencing technique converts non-invasive extracellular concentration sensors into dynamic flux sensors for measuring transport from the membrane to the tissue scale. In this tutorial review, we discuss the use of self-referencing micro/nanosensors for measuring physiological activity of living cells/tissues in agricultural, environmental, and biomedical applications comprehensible to any scientist/engineer.     

A Double Cation–π-Driven Strategy Enabling Two-Dimensional Supramolecular Polymers as Efficient Catalyst Carriers

The cation–π interaction is a strong non-covalent interaction that can be used to prepare high-strength, stable supramolecular materials. However, because the molecular plane of a cation-containing group and that of aromatic structure are usually perpendicular when forming a cation–π complex, it is difficult to exploit the cation–π interaction to prepare a 2D self-assembly in which the molecular plane of all the building blocks are parallel. Herein, a double cation–π-driven strategy is proposed to overcome this difficulty and have prepared 2D self-assemblies with long-range ordered molecular hollow hexagons. The double cation–π interaction makes the 2D self-assemblies stable. The 2D self-assemblies are to be an effective carrier that can eliminate metal-nanoparticle aggregation. Such 2D assembly/palladium nanoparticle hybrids are shown to exhibit recyclability and superior catalytic activity for a model reaction.     

Doping transition metal in PdSeO3 atomic layers by aqueous cation exchange: A new doping protocol for a new 2D photocatalyst

Elemental doping confined in atomically-thin 2D semiconductors offers a compelling strategy for constructing high performance photocatalysts. Although impressive progress has been achieved based on co-thermolysis method, the choices of dopants as well as semiconductor hosts are still quite limited to yield the elaborate photocatalyst with atomic-layer-confined doping defects, owing to the difficulty in balancing the reaction kinetics of different precursors. This study shows that the cation exchange reaction, which is dictated by the Pearson's hard and soft acids and bases (HSAB) theory and allowed to proceed at mild temperatures, can be developed into a conceptually new protocol for engineering elemental doping confined in semiconductor atomic layers. To this aim, the two atomic layers of a new type of 2D photocatalyst PdSeO₃ (PdSeO₃ 2ALs, 1.1 nm) are created by liquid exfoliation and exploited as a proof-of-concept prototype. It is demonstrated that the Mn(II) dopants with controlled concentrations can be incorporated into PdSeO₃ 2ALs via topological Mn²⁺-for-Pd²⁺ cation exchange performed in water/isopropanol solution at 30 °C. The resulting Mn-doped PdSeO₃ 2ALs present enhanced capacity for driving photocatalytic oxidation reactions in comparison with their undoped counterparts. The findings here suggest that the new route mediated by post synthetic cation exchange promises to give access to manifold 2D confined-doping photocatalysts, with little perturbations on the thickness, morphology, and crystal structure of the atomically-thin semiconductor hosts.     

A Double Cation–π‐Driven Strategy Enabling Two‐Dimensional Supramolecular Polymers as Efficient Catalyst Carriers

The cation–π interaction is a strong non‐covalent interaction that can be used to prepare high‐strength, stable supramolecular materials. However, because the molecular plane of a cation‐containing group and that of aromatic structure are usually perpendicular when forming a cation–π complex, it is difficult to exploit the cation–π interaction to prepare a 2D self‐assembly in which the molecular plane of all the building blocks are parallel. Herein, a double cation–π‐driven strategy is proposed to overcome this difficulty and have prepared 2D self‐assemblies with long‐range ordered molecular hollow hexagons. The double cation–π interaction makes the 2D self‐assemblies stable. The 2D self‐assemblies are to be an effective carrier that can eliminate metal‐nanoparticle aggregation. Such 2D assembly/palladium nanoparticle hybrids are shown to exhibit recyclability and superior catalytic activity for a model reaction.     

Molecular and crystal structure of 1-amino-X-pyrazinium mesitylenesulfonates

X-Ray diffraction analysis was performed of 1-amino-X-pyrazinium mesitylenesulfonates (X=H, 2-NH₂, 3-NHCOMe, 3-OMe, 3-Cl). In all events save 1,2-diaminopyrazinium cation the bond length of N-NH₂ was shorter than that of N-N bond but considerably longer than the length of the double bond N=N. In the 1,2-diaminopyrazinium cation the bond distance C²-NH₂ was close to the length of a common double bond C=N indicating the iminium character of the cation. Quantum-chemical calculations [AM1, PM3, DFT/(PBE/3z), B3LYP/6-31G++(2d,p)] provided the geometry of cations similar to the experimental one. In the crystals under investigation motifs were observed of 0D, 1D, and 2D type mainly due to hydrogen bonds N-H···O and π-stacking interactions of the aromatic rings.     

Interfacing Microbial Styrene Production with a Biocompatible Cyclopropanation Reaction

The introduction of new reactivity into living organisms is a major challenge in synthetic biology. Despite an increasing interest in both the development of small‐molecule catalysts that are compatible with aqueous media and the engineering of enzymes to perform new chemistry in vitro, the integration of non‐native reactivity into metabolic pathways for small‐molecule production has been underexplored. Herein we report a biocompatible iron(III) phthalocyanine catalyst capable of efficient olefin cyclopropanation in the presence of a living microorganism. By interfacing this catalyst with E. coli engineered to produce styrene, we synthesized non‐natural phenyl cyclopropanes directly from D ‐glucose in single‐vessel fermentations. This process is the first example of the combination of nonbiological carbene‐transfer reactivity with cellular metabolism for small‐molecule production.     

Inhibition of the formation and decay of stilbene core radical cations by the dendron during the photoinduced electron transfer

Formation and decay processes of stilbene core radical cation (ST*+) during the photoinduced electron transfer have been studied for a series of stilbene bearing benzyl ether-type dendrons (D). ST*+ and the radical cation of peripheral dendron (D*+) were generated by intermolecular hole transfer from biphenyl radical cation, which was generated from photoinduced electron transfer from biphenyl to the singlet-excited 9,10-dicyanoanthracene in a mixture of acetonitrile and 1,2-dichloroethane (3:1). An intramolecular dimer radical cation of benzyl groups at the terminal of stilbene dendrimer was indicated as a hole trapping site. Subsequent hole transfer from the trapping site to the core ST generated ST*+. The shielding effects of D depending on the dendrimer generation on the growth and decay of ST*+ were observed. It was revealed for the first time that D acts as the hole trapping site and the hole conductor on the way of the exothermic hole transfer from the terminal of D to the central core ST. We also found that D inhibits the charge recombination with 9,10-dicyanoanthracene radical anion because of the steric hindrance.     

Charge delocalization in self-assembled mixed-valence aromatic cation radicals

The spontaneous assembly of aromatic cation radicals (D(+?)) with their neutral counterpart (D) affords dimer cation radicals (D(2)(+?)). The intermolecular dimeric cation radicals are readily characterized by the appearance of an intervalence charge-resonance transition in the NIR region of their electronic spectra and by ESR spectroscopy. The X-ray crystal structure analysis and DFT calculations of a representative dimer cation radical (i.e., the octamethylbiphenylene dimer cation radical) have established that a hole (or single positive charge) is completely delocalized over both aromatic moieties. The energetics and the geometrical considerations for the formation of dimer cation radicals is deliberated with the aid of a series of cyclophane-like bichromophoric donors with drastically varied interplanar angles between the cofacially arranged aryl moieties. X-ray crystallography of a number of mixed-valence cation radicals derived from monochromophoric benzenoid donors established that they generally assemble in 1D stacks in the solid state. However, the use of polychromophoric intervalence cation radicals, where a single charge is effectively delocalized among all of the chromophores, can lead to higher-order assemblies with potential applications in long-range charge transport. As a proof of concept, we show that a single charge in the cation radical of a triptycene derivative is evenly distributed on all three benzenoid rings and this triptycene cation radical forms a 2D electronically coupled assembly, as established by X-ray crystallography.     

Extracellular Matrix Containing in vitro Three‐dimensional Tumor Models in Photodynamic Therapy‐related Research

Three‐dimensional (3D) tumor models have been intensively evaluated for their use in cancer research, and there is a strong rationale behind using 3D cell cultures in photodynamic therapy (PDT)‐related experimentation. In this contribution, it is explained why 3D cell cultures containing extracellular matrix (ECM) are preferred for this purpose. Results of experimental studies utilizing ECM‐containing 3D cellular models in PDT research are summarized. Finally, the design of in vitro 3D models that would provide clinically relevant information is discussed.