Covalent organic frameworks (COFs) have emerged as a promising light-harvesting module for artificial photosynthesis and photovoltaics. For efficient generation of free charge carriers, the ...donor-acceptor (D-A) conjugation has been adopted for two-dimensional (2D) COFs recently. In the 2D D-A COFs, photoexcitation would generate a polaron pair, which is a precursor to free charge carriers and has lower binding energy than an exciton. Although the character of the primary excitation species is a key factor in determining optoelectronic properties of a material, excited-state dynamics leading to the creation of a polaron pair have not been investigated yet. Here, we investigate the dynamics of photogenerated charge carriers in 2D D-A COFs by combining femtosecond optical spectroscopy and non-adiabatic molecular dynamics simulation. From this investigation, we elucidate that the polaron pair is formed through ultrafast intra-layer hole transfer coupled with coherent vibrations of the 2D lattice, suggesting a mechanism of phonon-assisted charge transfer.
Summary
Direct conversion of sunlight into value‐added chemicals through artificial photosynthesis has been recognized as one of the most promising ways to address the global energy needs and to ...utilize the sustainable energy source. Even though the various semiconducting materials have been used for the solar‐driven production of chemicals, many experimental efforts have been still focusing on developing clean and reusable photocatalysts. In this study, we report the new metal‐free graphitic carbon nitride (g‐C3N4) composite including anthracene moieties as a primary photosensitizer. The morphological and electronic structure of anthracene‐based g‐C3N4 (An‐g‐C3N4) composite were characterized by optical spectroscopies, electrochemical measurements, and theoretical calculations based on density‐functional theory. The An‐g‐C3N4 composite exhibited outstanding photocatalytic efficiency for the regenerations of NAD(P)H cofactors owing to the prominent charge‐transferred character and the superb light absorption. This study demonstrates that the catalytic reaction employing the combination of An‐g‐C3N4 photocatalyst and Z‐scheme nature would be a suitable option for artificial photosynthesis.
To directly convert solar energy into chemical energy, we synthesized the metal‐free graphitic carbon nitride (g‐C3N4) photocatalyst incorporated with anthracene moiety. By mimicking the natural photosynthesis based on Z‐scheme nature, we designed the artificial photosynthetic system consisted of the g‐C3N4 photocatalyst and the electron mediator. This system showed the superb conversion efficiency for the regeneration of NAD(P)H as well as for the oxidation of sulfide.
Abstract
Ultrafast motion of molecules, particularly the coherent motion, has been intensively investigated as a key factor guiding the reaction pathways. Recently, X-ray free-electron lasers (XFELs) ...have been utilized to elucidate the ultrafast motion of molecules. However, the studies on proteins using XFELs have been typically limited to the crystalline phase, and proteins in solution have rarely been investigated. Here we applied femtosecond time-resolved X-ray solution scattering (fs-TRXSS) and a structure refinement method to visualize the ultrafast motion of a protein. We succeeded in revealing detailed ultrafast structural changes of homodimeric hemoglobin involving the coherent motion. In addition to the motion of the protein itself, the time-dependent change of electron density of the hydration shell was tracked. Besides, the analysis on the fs-TRXSS data of myoglobin allows for observing the effect of the oligomeric state on the ultrafast coherent motion.
To meet the energy demands artificial photosynthesis is playing the most promising role these days. Using sunlight directly in a manner that can provide useful chemicals is a sustainable means of ...generating energy. Studies are going on in this context to make better and effective photocatalyst. In this paper, we study the synthesis of flower‐like graphene quantum dots‐based fuschin (GQDF) photocatalyst from lemon, which is created by a green and sustainable process that is effective and environment friendly. The UV‐visible spectra of prepared GQDF showed a high molar extinction coefficient. A flower‐like GQDF photocatalyst has better catalytic efficiency for the selective creation and regeneration of the NAD(P)H cofactor. A newly designed flower‐like GQDF photocatalyst is used as one of its most effective photocatalysts as they have several additional applications in the removal of CO2 and aqueous contaminants like heavy metals.
We have prepared a flower‐like GQDF (graphene quantum dots‐based acid fuschin) for the regeneration of NADH. Under solar light irradiation, an electron is excited from the highest‐occupied molecular orbital to the lowest‐unoccupied molecular orbital. Afterward, the excited electron gets transferred, and get reduced. Finally, a proton is reduced and then transferred to NAD+ forming NADH. The acquired flower‐like GQDF photocatalyst has excellent light harvesting properties as well as outstanding photoelectric properties.
Summary
Development of ecofriendly and low‐cost highly efficient photocatalysis is of importance in the field of chemical synthesis. Currently, various metals‐based organic materials, metal oxide ...nanoparticles, and metal nanomaterials have been urbanized as light harvesting photocatalysts for direct carbon (C)‐hydrogen (H) arylation of aryl diazonium salts and heteroarenes. These light harvesting photocatalysts, however, still suffer from poor stability, reusability problem, high cost, or less selectivity. Herein, we report the fabrication of a novel chitosan‐based fluorescein isothiocyanate (CBFITC) film photocatalyst and demonstrate its tremendous photocatalytic activity, high yields (97 ± 0.015%), selectivity (99%), and reusability to catalyze the metal free solar‐light‐mediated direct CH arylation of aryl diazonium salts and heteroarenes at ambient temperature. Moreover, CBFITC film photocatalyst can be recycled more than five times without loss of activity, verifying this photocatalyst excellent light harvesting ability and stability. The present approach to fabricate a metal‐free film photocatalyst with the suitable band gap will be a new platform for efficient photocatalytic reaction and provide a new insight into the solar chemical synthesis.
Development of eco‐friendly and low‐cost highly efficient photocatalysis is very importance for organic transformations. Herein, we report chitosan‐based fluorescein isothiocyanate (CBFITC) film photocatalyst is the first‐time design to bring new insight into direct CH bond arylation under light irradiation. Therefore, CBFITC film photocatalyst has also a potential application in the field of medicinal and phermaceutical chemistry.
One of the most important questions in biological science is how a protein functions. When a protein performs its function, it undergoes regulated structural transitions. In this regard, to better ...understand the underlying principle of a protein function, it is desirable to monitor the dynamic evolution of the protein structure in real time. To probe fast and subtle motions of a protein in physiological conditions demands an experimental tool that is not only equipped with superb spatiotemporal resolution but also applicable to samples in solution phase. Time-resolved X-ray solution scattering (TRXSS), discussed in this Account, fits all of those requirements needed for probing the movements of proteins in aqueous solution. The technique utilizes a pump–probe scheme employing an optical pump pulse to initiate photoreactions of proteins and an X-ray probe pulse to monitor ensuing structural changes. The technical advances in ultrafast lasers and X-ray sources allow us to achieve superb temporal resolution down to femtoseconds. Because X-rays scatter off all atomic pairs in a protein, an X-ray scattering pattern provides information on the global structure of the protein with subangstrom spatial resolution. Importantly, TRXSS is readily applicable to aqueous solution samples of proteins with the aid of theoretical models and therefore is well suited for investigating structural dynamics of protein transitions in physiological conditions. In this Account, we demonstrate that TRXSS can be used to probe real-time structural dynamics of proteins in solution ranging from subtle helix movement to global conformational change. Specifically, we discuss the photoreactions of photoactive yellow protein (PYP) and homodimeric hemoglobin (HbI). For PYP, we revealed the kinetics of structural transitions among four transient intermediates comprising a photocycle and, by applying structural analysis based on ab initio shape reconstruction, showed that the signaling of PYP involves the protrusion of the N-terminus with significant increase of the overall protein size. For HbI, we elucidated the dynamics of complex allosteric transitions among transient intermediates. In particular, by applying structural refinement analysis based on rigid-body modeling, we found that the allosteric transition of HbI accompanies the rotation of quaternary structure and the contraction between two heme domains. By making use of the experimental and analysis methods presented in this Account, we envision that the TRXSS can be used to probe the structural dynamics of various proteins, allowing us to decipher the working mechanisms of their functions. Furthermore, when combined with femtosecond X-ray pulses generated from X-ray free electron lasers, TRXSS will gain access to ultrafast protein dynamics on sub-picosecond time scales.
Covalent perylene frameworks (CPFs) with melamine linkages have newly received rising interest for a variety of applications because of nitrogen‐rich content and high stability. Herein, we account a ...new simple strategy to in situ attain nitrogen‐rich covalent perylene frameworks (NRCPFs) as highly active photo platforms for in situ bond formation between aryldiazonium salts and heteroarenes (C–H bond arylation) through the controlled photoredox route.
C–H bond arylation between aryldiazonium salts and heteroarenes through in situ prepared NRCPFs photocatalyst under solar light irradiation. The NRCPFs photocatalyst has been more efficient due to the nitrogen enrich covalent perylene framework which is utilized for C–H bond arylation. C–H bond arylated products have a wide range of industrial and medicinal applications.
The Light-oxygen-voltage-sensing domain (LOV) superfamily, found in enzymes and signal transduction proteins, plays a crucial role in converting light signals into structural signals, mediating ...various biological mechanisms. While time-resolved spectroscopic studies have revealed the dynamics of the LOV-domain chromophore’s electronic structures, understanding the structural changes in the protein moiety, particularly regarding light-induced dimerization, remains challenging. Here, we utilize time-resolved X-ray liquidography to capture the light-induced dimerization of Avena sativa LOV2. Our analysis unveils that dimerization occurs within milliseconds after the unfolding of the A’α and Jα helices in the microsecond time range. Notably, our findings suggest that protein-protein interactions (PPIs) among the β-scaffolds, mediated by helix unfolding, play a key role in dimerization. In this work, we offer structural insights into the dimerization of LOV2 proteins following structural changes in the A’α and Jα helices, as well as mechanistic insights into the protein-protein association process driven by PPIs.Here, the authors provide mechanistic insight into light-induced dimerization of a Light-Oxygen-Voltage (LOV) domain using time-resolved X-ray liquidography, furthering our understanding LOV domain photoactivation and protein-protein interaction-driven oligomerization.
PDF
