Photoswitchable fluorescent molecules (PSFMs) are important tools for fluorescence imaging of biomolecules. To date, PSFMs have been applied for pulse-chase experiments and super-resolution imaging. However, most have limitations in that their fluorophores have low photostability or require cytotoxic additives. Here, we have developed PSFMs using a photochromic compound, arylazopyrazole, to overcome these limitations. These molecules showed reversible changes in fluorescence intensity upon photoirradiation and high photostability in aqueous solutions.
Membrane-integrated nitric oxide reductases (NOR) catalyze the formation of nitrous oxide (N2O) from two NO molecules using two protons and two electrons at a heme/non-heme iron binuclear center. Despite extensive efforts, the mechanism underlying the NOR-catalyzed reaction has been poorly understood due to the rapidity of the reaction. Here, we utilized a photosensitive caged NO compound as a trigger for the NOR reaction to characterize the NO reduction mechanism by time-resolved visible absorption spectroscopy. We showed that the NOR reaction consists of three steps. One NO molecule binds to the reduced binuclear center to form a non-heme Fe(II)-NO species in the 1st phase (microsecond timescale), followed by a migration of NO to form the other chemical species, possibly 5-coordinate heme b3-NO, in the 2nd phase (timescale of tens of microseconds). Then, the NO bound to heme reacts with a second NO molecule in the 3rd phase (millisecond timescale), in which protonation and electron transfer promote N-N bond formation and N-O bond cleavage to yield N2O. These findings led us to propose a revised trans mechanism for NO reduction by NOR.
Chiral surface ligands have often been employed to impart optical activity to metal nanoclusters, metal nanoparticles and semiconductor nanocrystals. They are considered to form a chiral structure to a certain degree whereas the effect of such chiral structure on the global physicochemical properties apart from chiroptical ones has been unexplored. We herein demonstrate the impact of optical purity of chiral surface ligand on the emission property of silver nanocluster (NCs). Chiral bidentate α-dihydrolipoic acid (DHLA) with varied enantiomeric excess (ee) values was employed as a surface capping ligand to prepare a series of silver NCs, displaying identical absorption and emission profiles typical for Ag29 NCs. Interestingly, the emission quantum yields exhibited a clear dependence on the enantiopurity of DHLA. The more enantiopure DHLA afforded more emissive NCs. This |ee|-dependent emission efficiency was discussed in association with the orientation of ligands on the Ag29 NCs. The surface structures of Ag29(dithiolate)12 models composed of enantiopure and racemic ligand systems were compared with the aid of DFT calculations, suggesting that the enantiopure surface is more stable with one-handed ligand orientation. Two-dimensional NMR technique also supported the observation that well-defined ligand orientations depend on the enantiomeric composition of chiral ligand.
A solvent selection scheme for optimization of reactions is proposed using machine learning, based on the numerical descriptions of solvent molecules. Twenty-eight key solvents were represented using 17 physicochemical descriptors. Clustering analysis results implied that the descriptor represents the chemical characteristics of the solvent molecules. During the assessment of an organometallic reaction system, the regression analysis indicated that learning even a small number of experimental results can be useful for identifying solvents that will produce high experimental yields. Observation of the regression coefficients, and both clustering and regression analysis, can be effective when selecting a solvent to be used for an experiment.
In a simple and versatile reprocessing method for recycling U and Pu from spent nuclear fuels, cyclic amides like N-alkylated 2-pyrrolidone derivatives (NRPs) are exclusively employed. However, there has been no convincing rational to explain why such a heterocyclic structure is required. To answer this question, we employed N-cyclohexyl-2-pyrrolidone (NCP) and N-cyclohexylformamide (NCF) as cyclic and acyclic monodentate amides, and focused on the following 3 topics in this study; (1) structural chemistry of their uranyl dinitrato complexes, (2) precipitation behavior of UO22+ from HNO3(aq) by using these amides, and (3) their chemical stability in HNO3(aq) simulating the reprocessing conditions for spent nuclear fuels. Fundamental coordination chemistry of UO2(NO3)2(L)2 (L = NCP, NCF) was found to be common to both L, regardless of the presence or absence of the pyrrolidone ring. Furthermore, both L exhibit comparable capability in precipitation of UO22+ from HNO3(aq). The most critical difference between NCP and NCF was found in their chemical stability in HNO3(aq), where NCF was gradually decomposed through acid-catalyzed hydrolysis, while NCP remained intact for at least 4 h. In conclusion, the pyrrolidone ring of NRPs plays an important role to sterically protect the carbonyl C from nucleophilic hydrolysis which initiates the amide C(=O)–N bond cleavage.
A solid-electrolyte interphase (SEI) is widely recognized to improve the safety and durability of lithium ion batteries. In this work, we investigate the structure and chemistry of the carbon electrode and SEI in operando during two-cycle battery operation for further understanding of the electrochemical reactions, and the effect of the hysteresis using in situ neutron reflectivity (NR) and ex situ hard X-ray photoelectron spectroscopy (HAXPES). The results revealed the structural evolution of the electrode and SEI layer, such as the change in the thickness and scattering length density (SLD) in connection with the chemical composition during the lithiation/delithiation processes. Next, the HAXPES results at the point before and after the charging/discharging process revealed the change in the chemical composition of the SEI layer due to the chemical reactions on the formation/degradation. Based on the combination of these analyses, the results showed that the SLDs of the SEI layer evaluated by NR analysis were consistent with those determined by HAXPES. Concerning the difference in the first and second cycles, the structure of the amorphous carbon electrode exhibited hysteresis due to lithiation/delithiation, whereas the chemical composition of the SEI layer after charge/discharge was almost independent of the number of cycles.
In this study we demonstrate that organic radical photopolymerized resins hybridized with inorganic silica nanoparticles improve the mechanical strength of replica mold materials and that organic-inorganic hybridization prolongs mold lifetime independently of mold linewidth during step-and-repeat UV nanoimprinting over 100 cycles. Silica nanoparticles with polymerizable methacryloyl groups (NPMC) were added to 1,10-decanediol dimethacrylate (MC10) and diacrylate (AC10) base monomers to enhance the mechanical properties of the replica molds. Heterogeneous combination of polymerizable groups, such as AC10 and NPMC, maintained a fluidity suitable for molding in UV nanoimprinting, and enabled the preparation of hybrid replica materials with a high inorganic silica content of 56.9 wt% (37.0 vol%). Nanoindentation measurements revealed that the hybrid replica materials with 37.0 vol% silica showed a Young’s modulus of 4.4 GPa. Only the 45-nm-linewidth patterns of AC10-based replica molds without NPMC showed line-collapse defects after imprint cycle tests, while the 45- and 100-nm-linewidth shapes of the hybrid resin materials with NPMC remained intact after 128 step-and-repeat imprint cycles and nanoindentation measurements.
Three new dyes 1–3 derived from indol-carbohydrazide and azo-azomethine for the optical detection of F− ion have been developed. Dye 1 was found to be an effective colorimetric sensor for F− ion response with over 250 nm red-shift. Moreover, the resultant dye•••HF2− complex (dye-F) could be successfully used as a secondary sensor for analyzing trace water in aprotic organic solvents especially in acetonitrile with a low limit of detection. In addition to detection of low-level water content in solution, test paper incorporated with 1-F complex or 2-F complex was well developed for naked-eye detection of water content in four organic solvents as mentioned above. Importantly, the test paper prepared by introducing 1-F complex or 2-F complex could be developed to prepare an ink-free rewritable paper by using water as the sole trigger. Furthermore, the same test paper could still work for many cycles without obvious loss in color quality.
Combined-permutation representations (CPRs) for characterizing D3h-skeletons (i.e., a cyclopropane skeleton, a trigonal bipyramidal skeleton, an iceane skeleton, and so on) are constructed by starting from respective sets of generators, where the permutation of each generator is combined with a mirror-permutation of 2-cycles to give the CPR of degree 8 (= 6 + 2) for the cyclopropane skeleton, the CPR of degree 7 (= 5 + 2) for the trigonal bipyramidal skeleton, the CPR of degree 14 (= 12 + 2) for the iceane skeleton, and so on. Mark tables (tables of marks) of these CPRs are different in the alignment of subgroups from each other when they are produced as primary mark tables by the GAP system. On the other hand, the GAP functions MarkTableforUSCI and constructUSCITable, which have been previously developed to systematize the concordant construction of a standard mark table and a standard USCI-CF (unit-subduced-cycle-index-with-chirality-fittingness) table, are capable of constructing the standard mark table and the standard USCI-CF table even if we start from any of these CPRs. After a set of PCI-CFs (partial cycle indices with chirality fittingness) is calculated for each skeleton by means of the newly-developed GAP functions, symmetry-itemized combinatorial enumeration is conducted by means of the PCI method of Fujita’s USCI approach (S. Fujita, Symmetry and Combinatorial Enumeration in Chemistry, Springer-Verlag, Berlin-Heidelberg, 1991).
This study investigated the adsorption of a non-ionic water-insoluble organic molecule (meso-tetraphenylporphyrin, TPP) on a trioctahedral layered aluminosilicate (saponite, SP) in organic solvents in order to investigate properties of SP as an adsorbent for a wider variety of molecules, other than cationic or polar ones. The affinity of solvents for the layered aluminosilicate surface was an important factor for predicting the molecule’s adsorption proprieties. Namely, solvents with low affinity for the aluminosilicate should be selected so that molecules can approach the surface, thus prompting adsorption of the molecules. Under these conditions, TPP was adsorbed to SP due to their basicity and acidity. The acid on SP adsorbing TPP was revealed to be Lewis acid. The weaker acid strength (H0, estimated to be 0.8–1.5) compared with that of Brønsted acids appeared to be more suitable for adsorbents because molecules are recovered efficiently from SP where their intramolecular charge distributions are shifted. The acidity of SP is discussed quantitatively in this study because this has not been done thoroughly in comparison with dioctahedral aluminosilicates such as montmorillonite, which are conventionally used as catalysts.
Light-induced difference Fourier-transform infrared (FTIR) spectroscopy is a powerful, sensitive and informative method for studying protein structural changes in photoreceptive proteins. Strong absorption of water in the IR region is always an issue in this method. However, if water content in the sample is controlled during measurements, this method can provide detailed structural information on a single protein-bound water molecule. We optimized the measuring conditions of light-induced difference FTIR spectroscopy to hydrated film samples. In doing so, highly accurate difference FTIR spectra were successfully obtained for a light-driven proton-pump bacteriorhodopsin (BR), not only in the conventional 1800–800 cm−1 region, but also in the 4000–1800 cm−1 region. A highly accurate measuring system of light-induced difference FTIR spectroscopy was applied to various photoreceptive proteins such as animal and microbial rhodopsins, and comprehensive FTIR analyses revealed that proton-pumping rhodopsins possess strongly hydrogen-bonded water molecules. It was concluded that a strongly hydrogen-bonded water molecule is the functional determinant of a proton pump. FTIR spectroscopy was also applied to flavin-binding photoreceptors, where we elucidated the molecular mechanisms of adduct formation in the LOV domain, hydrogen-bonding alteration in the BLUF domain, and activation and DNA-repair mechanisms in photolyases. In studies on rhodopsin, we contributed to the discovery and creation of new functions, where FTIR spectroscopy was used for the molecular characterization of new rhodopsins. These new rhodopsins offer promising tools in optogenetics that revolutionized brain sciences. As highlighted in this review article, we provided new insights into the structure/function relationship of biomolecules by unique difference FTIR spectroscopy. In particular, by studying photoreceptive proteins such as rhodopsins, we clarified the mechanism of how light is taken into proteins, and how it leads to their function.
A range of N,N-diarylthiazol-5-amines having a 4-pyridyl group on a thiazole ring were developed, and their photophysical properties were elucidated. Their synthesis was achieved by applying our methods to the combination of N-arylmethyl secondary thioamides and N,N-diarylthioformamides. This enabled us to obtain amines with different types of aromatic groups on the nitrogen atom. Their absorption and emission spectra in solution were examined. The 4-pyridyl group gives higher polarity to the amines. The solid-state emissions of the amines were also evaluated. Several amines showed mechanofluorochromism (MFC). A 4-pyridyl group on a thiazole ring was a requisite for the expression of MFC properties. Although N-(5-thiazolyl) N,N-di(2-naphthyl)amines did not exhibit MFC by grinding of the pristine powder, white-light emission was observed when the ground powder was fumed with acetone vapor.
A red-light-mediated Barton–McCombie reaction is described, in which chlorophyll a is used as a photocatalyst and tris(trimethylsilyl)silane or Hantzsch ester is used as the hydrogen source. The reaction can be performed with a set of easily available equipment and reagents, and a variety of linear and cyclic xanthates could be applied. In contrast to the traditional conditions, the reaction does not involve toxic organotin or an explosive radical initiator. The reaction mechanism was analyzed both by experiments and computation, and it was suggested that the radical chain mechanism initiated by excitation of complex followed by charge transfer is likely to be operative.