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Quantifying the Initial Unfolding of Bacteriorhodopsin Reveals Retinal Stabilization
摘要： The forces that stabilize membrane proteins remain elusive to precise quantification. Particularly important but poorly resolved are the forces present during a membrane protein’s initial unfolding, where the most native set of interactions are present. We developed a high-precision, atomic force microscopy assay to study the initial unfolding of bacteriorhodopsin. We discovered rapid near-equilibrium folding between the first three unfolding states that corresponded to the unfolding of 5 and 8 amino-acids respectively when using a cantilever optimized for 2-μs resolution. Interestingly, the third of these states was retinal stabilized and previously undetected despite being the most mechanically stable state in the whole unfolding pathway, supporting 150 pN for >1 min. We expect that this ability to measure the rapid and reversible dynamics in the initial unfolding of bacteriorhodopsin provides a platform for quantifying the energetics of membrane proteins under native-like conditions.
关键词： protein folding,single molecule force spectroscopy,site-specific bioconjugation,membrane proteins,atomic force microscopy
更新于2025-09-04 15:30:14
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Intrinsic and Extrinsic Heavy Atom Effect on the Multifaceted Emissive Behavior of Cyclic Triimidazole
摘要： Since heavy halogen atoms can be used to tune the emissive properties of organic luminogens, the understanding of their role in the photophysics is fundamental for materials engineering. Here, the extrinsic and intrinsic heavy atom effects on the photophysics of organic crystals are separately evaluated by comparing cyclic triimidazole (TT) with its mono-iodo derivative (TTI) and its cocrystal with diiodotetrafluorobenzene (TTCo). Crystals of TT show room temperature ultralong phosphorescence (RTUP) originated from H-aggregation. TTI and TTCo display two additional long lived components whose origin is elucidated through single crystal X-ray and DFT-TDDFT studies. The results highlight the different effects of the I atom on the three phosphorescent emissions. Intrinsic heavy atom effects play a major role on molecular phosphorescence which is displayed at RT only for TTI. H-aggregate RTUP and the I···N XB induced phosphorescences on the other side depend only on packing features.
关键词： photophysics,co-crystal,room temperature phosphorescence,halogen bonding,time resolved spectroscopy
更新于2025-09-04 15:30:14
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Correlation between the structure and structural relaxation data for (GeSe2)y(Sb2Se3)1-y glasses
摘要： Combined calorimetric and structural study, employing the techniques of differential scanning calorimetry and Raman spectroscopy, was performed to describe the enthalpy relaxation processes in the (GeSe2)y(Sb2Se3)1-y chalcogenide glasses. The full glass forming compositional region (y = 0.3–0.9) was explored. The enthalpy relaxation was described in terms of the phenomenological Tool-Narayanaswamy-Moynihan model. Compositional evolution of the glass transition temperatures and relaxation activation energies was explained based on the changing average bond energies and overall interconnectivity of the glassy matrices. Resemblance between the activation energies of the relaxation processes and viscous flow was confirmed for all studied glasses. Non-linearity and non-exponentiality of the enthalpy relaxation were found to be invariant with composition. The structural relaxation kinetics as well as kinetic fragilities determined for the present (GeSe2)y(Sb2Se3)1-y glassy system were very similar to the results obtained earlier for the (GeS2)y(Sb2S3)1-y glasses, which can be attributed to the similarly constrained topology of the pseudo-binary compositional lines.
关键词： Enthalpy relaxation,Raman spectroscopy,TNM model,Ge-Sb-Se glasses,DSC
更新于2025-09-04 15:30:14
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Interface Properties of GaP/Si Heterojunction Fabricated by PE-ALD
摘要： The properties of n-GaP/p-Si interface as well as their influence on solar cell performance are studied for GaP layers grown by low-temperature (380 °C) plasma-enhanced atomic layer deposition (PE-ALD). The influence of different plasma treatments and RF power values are explored. The increase of RF power leads to a growth transition from amorphous (a-GaP) to microcrystalline GaP (μc-GaP) with either amorphous-GaP/Si or epitaxial-GaP/Si interface, respectively. However, when continuous hydrogen plasma is used the amorphous-GaP/Si interface exhibits better photovoltaic performance compared to the epitaxial one. Values of open circuit voltage, Voc ? 0.45–0.55 V and internal quantum efficiencies, IQE > 0.9 are obtained for amorphous-GaP/Si interfaces compared to Voc ? 0.25–0.35 V and IQE < 0.45 for epitaxial-GaP/Si interfaces. According to admittance spectroscopy and TEM studies the near-surface (30–50 nm) area of the Si substrate is damaged during growth with high RF power of hydrogen plasma. A hole trap at the level of EV t (0.33 ± 0.02) eV is detected by admittance spectroscopy in this damaged Si area. The damage of Si is not observed by TEM when the deposition of the structures with epitaxial-GaP/Si interface is realized by a modified process without hydrogen plasma indicating that the damage of the near-surface area of Si is related to hydrogen plasma interaction.
关键词： admittance spectroscopy,solar cells,PE-ALD,interface,GaP/Si heterojunction
更新于2025-09-04 15:30:14
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Ultrafast Excited State Dynamics of a Stilbene–Viologen Charge Transfer Complex and Its Interaction with Alkanediammonium Salts
摘要： The spectral and thermodynamic properties of charge transfer complexes D?A and D?A?D between (E)-bis(18-crown-6)stilbene (D) and 1,1'-bis(2-ammonioethyl)-4,4'-bipyridinium tetraperchlorate (A) in MeCN were studied. The complex D?A is highly stable, while the complex D?A?D is weakly stable. D?A does not fluoresce due to fast intramolecular processes of direct and reverse electron transfer. The efficiency of D?A fluorescence ignition upon adding alkanediammonium salts depends on the length of a carbon chain. The spectral and kinetic characteristics of D?A and D?A?D CT states were obtained by femtosecond transient absorption spectroscopy. It was established that the characteristic time of back electron transfer in the CT state of D?A?D (770 fs) is significantly higher than that in the CT state of D?A (400 fs). In a number of charge transfer complexes, formed by derivatives of 4,4'-bipyridinium and di-(4-pyridinium)-ethylene with ammonioethyl and ammoniopropyl N-substituents, the rate of back electron transfer depends weakly on the acceptor nature, but is determined by the length of the carbon chain of terminal groups.
关键词： fluorescence,charge transfer complex,ultrafast electron transfer,transient absorption spectroscopy,bis-crown ether
更新于2025-09-04 15:30:14
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Preparation, characterization and electrical behaviors of PEDOT:PSS-Au/Ag nanocomposite thin films: an ecofriendly approach
摘要： Structure, morphology and electrical behaviors of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) or PEDOT:PSS thin films are investigated in the presence of protein-mediated green chemically synthesized positively charged gold and silver nanoparticles. The pure and PEDOT:PSS nanocomposite thin films are prepared by spin coating method. The presence of both nanoparticle and polymer is confirmed from X-ray diffraction, whereas composite formation is confirmed from Raman and FTIR spectroscopy. Atomic force microscopy (AFM) images show the surface morphologies of both pure and composite films, whereas average film thicknesses are obtained from AFM and X-ray reflectivity analysis. The presence of electrostatic interaction between the positively charged metallic nanoparticles and negatively charged PSS chains leads to the electrostatic shielding between cationic PEDOT and anionic PSS, which favors better charge transfer through PEDOT–PEDOT conducting paths. The increase in electrical conductivity is visualized from the current–voltage (I–V) curves, which show that the conductivity is relatively higher in the presence of silver than gold nanoparticles in the composite thin films. The conductivity of nanocomposite films is approximately five to six times enhanced in comparison with the pristine PEDOT:PSS thin films.
关键词： FTIR spectroscopy,PEDOT:PSS-Au/Ag thin films,AFM,UV–Vis,Nanocomposites,Conductivity
更新于2025-09-04 15:30:14
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Flattened fiber-optic ATR sensor enhanced by silver nanoparticles for glucose measurement
摘要： This paper proposes a novel fiber attenuated total reflection (ATR) sensor with silver nanoparticles (AgNPs) on the flattened structure based on mid-infrared spectroscopy for detecting low concentration of glucose with high precision. The flattened structure was designed to add the effective optical path length to improve the sensitivity. AgNPs were then deposited on the surface of the flattened area of the fiber via chemical silver mirror reaction for further improving the sensitivity by enhancing the infrared absorption. Combining the AgNPs modified flattened fiber ATR sensor with a CO2 laser showed a strong mid-infrared glucose absorption, with an enhancement factor of 4.30. The glucose concentration could be obtained by a five-variable partial least-squares model with a root-mean-square error of 4.42 mg/dL, which satisfies clinical requirements. Moreover, the fiber-based technique provides a pretty good method to fabricate miniaturized ATR sensors that are suitable to be integrated into a microfluidic chip for continuous glucose monitoring with high sensitivity.
关键词： Attenuated total reflection sensor,Mid-infrared spectroscopy,Flattened structure,AgNPs,Continuous glucose monitoring
更新于2025-09-04 15:30:14
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Transport properties of Cu-AlF3-W and Cu-AlF3-Cu heterojunctions using STS measurements and a DFT-NEGF approach
摘要： To understand and to analyze the transport properties of different metal-insulator systems, we developed an experimental study of the electronic transport properties of AlF3 thin films deposited over a Cu(1 0 0) substrate, and a theoretical study to model systems composed by an AlF3 molecule between two metallic Cu(1 0 0)-W(1 0 0) and Cu(1 0 0)-Cu(1 0 0) electrodes with different geometries. The left common electrode is always a Cu(1 0 0) layer, meanwhile the right changing electrode, W(1 0 0) or Cu(1 0 0), in some cases is represented as a layer and in others as having a tip ending. Tunnelling current against voltage (I-V) characteristic curves have been obtained by Scanning Tunneling Spectroscopy (STS) measurements and computed using density functional theory (DFT) with the non equilibrium Green function method (NEGF) within a bias voltage range from ?2.5 to 5.0 V. The theoretical curves show low current values, in the order of 10?12 to 10?9, in good agreement with the I-V experimental curves in the same range. This reveals that breakdown response currents begin at higher voltages than 5.0 V. The transmission spectrum, total (DOS) and partial (PDOS) density of states are also presented being the transmission variations addressed in terms of the DOS.
关键词： Scanning Tunneling Spectroscopy (STS),Non Equilibrium Green Functions (NEGF),Scanning Tunneling Microscopy (STM),Electronic transport,AlF3 thin films
更新于2025-09-04 15:30:14
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Stability and Reactivity of Silicon Magic Numbers Doped with Aluminum and Phosphorus Atoms
摘要： The progressive scaling down of the silicon-based electronics has allowed to develop devices at nanometer scale, requiring new engineering techniques guided by fundamental chemical and physical concepts. Particularly, the nanostructured cluster systems are promising materials since their physical-chemical properties are sensitive to its shape, size and chemical components, such that completely different materials can be produced by the simple addition or removal of a single atom. These size-tunable properties can open a new area in materials science and engineering. In the present work, quantum chemical methods were used to study the chemical substitution effects caused by subvalent (aluminum) and supervalent (phosphorus) atoms in the physical-chemical properties of some small silicon clusters which demonstrate high stability, called magic numbers. The changes in the electronic structure and chemical acceptance to the dopants were evaluated with respect to: ionization potential, electronic excitation energy, stability and reactivity parameters. Taken together, these results enable to identify the most stable silicon-doped clusters. Regarding electrophilic reactions, Si10P is the most favorable system, while for nucleophilic reactions, none of the doped clusters resulted in higher stability.
关键词： Aluminum,Silicon Magic Numbers,Quantum Chemistry,Spectroscopy,Molecular Structure,Phosphorus Atoms
更新于2025-09-04 15:30:14
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Development of Thermal Kinetic Inductance Detectors Suitable for X-ray Spectroscopy
摘要： We report on the development of thermal kinetic inductance detectors (TKIDs) suitable to perform X-ray spectroscopy measurements. The aim is to implement MKIDs sensors working in thermal quasi-equilibrium mode to detect X-ray photons as pure calorimeters. The thermal mode is a variation on the MKID classical way of operation that has generated interest in recent years. TKIDs can offer the MKIDs inherent multiplexibility in the frequency domain, a high spatial resolution comparable with CCDs, and an energy resolution theoretically limited only by thermodynamic fluctuations across the thermal weak links. Microresonators are built in Ti/TiN multilayer technology with the inductive part thermally coupled with a metal absorber on a suspended SiN membrane, to avoid escape of phonons from the film to the substrate. The mid-term goal is to optimize the single-pixel design in terms of superconducting critical temperatures, internal quality factors, kinetic inductance and spectral energy resolution. The final goal is to realize a demonstrator array for a next generation thousand pixels X-ray spectrometer. In this contribution, the status of the project after one year of developments is reported, with detailed reference to the microresonators design and simulations and to the fabrication process.
关键词： Thermal mode,Microwave kinetic inductance detectors,TKID,MKIDs,Thin film,X-ray spectroscopy,Superconducting film,Micromachining,Super-conductive microresonators,Thermal kinetic inductance detectors
更新于2025-09-04 15:30:14