An unprecedented substrate-selective catalytic enhancement effect of an alkanethiol-self-assembled monolayer (SAM) on Au nanoparticles (AuNPs) is reported. In the supported 2D-array of AuNPs, the alkanethiol-SAM acts as a protein-like soft reaction space in which the substrate molecules are encapsulated through non-covalent intermolecular hydrophobic interactions, and thus catalytic reactions are accelerated at AuNP surfaces.
We demonstrate a bottom-up approach to fabricating a visible light-driven titania photocatalyst device bearing an embedded two-dimensional (2D) array of gold nanoparticles (AuNPs) as a near-field light-generating layer. The device is a layered structure prepared by depositing a 2D array of AuNPs on a transparent conductive substrate (10 nm indium tin oxide (ITO) layer on quartz), coating the 2D array of AuNPs with a monolayer of trimethoxyoctylsilane (TMOS), and depositing titania nanocrystals on the anchoring molecule (TMOS) layer. The visible light activity of the device was tested using photocatalytic degradation of methylene blue (MB) by illuminating the device with visible light (700 nm light) and ultraviolet (UV) light (250-380 nm). The localized surface plasmon resonance peak of the 36 nm AuNP 2D array is around 700 nm with a full-width at half-maximum of 350 nm. In comparison with other control samples, the device showed the highest photocatalytic activity with visible irradiation, which was 1.7 times higher than that of titania with UV irradiation. The origin of the visible light activity was confirmed by both quadratic incident light power dependency and action spectrum to be plasmon-induced (near-field enhancement by AuNPs) two-photon absorption.
Stimuli-responsive supramolecular assembly has been studied extensively as a forward-looking technology for the precise control of the physical properties and functions of aggregates. [1][2][3] Recently, it was found that a blast of ultrasound can act as a trigger for the instant gelation of stable organic fluids when a small amount of a clothespin-shaped dinuclear palladium complex is used as a type of switchable gelator. [4,5] The ultrasound waves were thought to cleave the intramolecular p-stacking interactions of the complexes, inducing rapid and spontaneous aggregation through interpenetrating stacking interactions. Now this self-lock/interlock switching has been carried out with hydrogen-bonded aggregates, using the newly designed metalated dipeptide 1 a (Fmoc = 9-fluorenylmethyloxycarbonyl). This work is expected to provide a new methodology for the creation of stimuli-responsive H-bonded supramolecular assemblies, [1b-f, 2b-d] especially those containing peptide nanoarchitectures. [1c-f, 2c, 6] This paper describes the sound-induced gelation of palladium-bound peptides, and the precise control of their switchable aggregation by the tuning of sound factors.Brief ultrasound irradiation (0.45 W cm À2 , 40.0 kHz, 60 s) of a homogeneous 1.50 10 À2 m solution of dipeptide 1 a (n = 2, X = Cl) in EtOAc turned the stable pale-yellow solution into a stable opaque gel (Figure 1). Gelation was observed exclusively when ultrasound was used as an external stimulus, and spontaneous aggregation or formation of pregels did not occur without sonication. When nonsonicated samples were cooled or left to stand for a long time, ordinary precipitation of a small amount of amorphous solids or crystals resulted. Gels formed by sonication were stable but were readily converted to the original stable solutions upon heating and subsequent cooling to room temperature. This switchable solgel transition occurred exclusively when esters or chlorobenzene were used as solvents, while other solvents such as benzene, toluene, acetone, and acetonitrile did not provide gels regardless of concentration and sonication conditions. The chloro ligand and the short methylene spacer have proven to be indispensable for this switchable gelation. Typically, the dipeptidyl NCS complex 1 b and the Cl complex with longer spacer 1 c did not cause the gelation of any organic solvents. Also, solutions of amino acid 2, tripeptide 3, and tetrapeptide 4 in various organic solvents were stable under similar sonication conditions. Kinetic studies on the gelation of a 7.00 10 À3 m solution of 1 a in [D 8 ]EtOAc at 25 8C after sonication (0.45 W cm À2 , 43.5 kHz) were carried out by means of 1 H NMR (500 MHz) analysis, in which mobile, unaggregated 1 a in sol and gel states could be observed as distinct detectable species similar to conventional gelators. [7] The time dependence of the concentration of 1 a during the entire gelation process indicated that gelation began immediately after sonication, and proceeded until 1 a was almost completely consumed ( Figure...
We have developed a novel diastereoselective iron-catalyzed cross-coupling reaction of various glycosyl halides with aryl metal reagents for the efficient synthesis of aryl C-glycosides, which are of significant pharmaceutical interest due to their biological activities and resistance toward metabolic degradation. A variety of aryl, heteroaryl, and vinyl metal reagents can be cross-coupled with glycosyl halides in high yields in the presence of a well-defined iron complex, composed of iron(II) chloride and a bulky bisphosphine ligand, TMS-SciOPP. The chemoselective nature of the reaction allows the use of synthetically versatile acetyl-protected glycosyl donors and the incorporation of various functional groups on the aryl moieties, producing a diverse array of aryl C-glycosides, including Canagliflozin, an inhibitor of sodium-glucose cotransporter 2 (SGLT2), and a prevailing diabetes drug. The cross-coupling reaction proceeds via generation and stereoselective trapping of glycosyl radical intermediates, representing a rare example of highly stereoselective carbon-carbon bond formation based on iron catalysis. Radical probe experiments using 3,4,6-tri-O-acetyl-2-O-allyl-α-d-glucopyranosyl bromide (8) and 6-bromo-1-hexene (10) confirm the generation and intermediacy of the corresponding glycosyl radicals. Density functional theory (DFT) calculations reveal that the observed anomeric diastereoselectivity is attributable to the relative stability of the conformers of glycosyl radical intermediates. The present cross-coupling reaction demonstrates the potential of iron-catalyzed stereo- and chemoselective carbon-carbon bond formation in the synthesis of bioactive compounds of certain structural complexity.
Innovative nanophotonic applications require a technique for generating not a nanometer-scale point but a large-area (mm2−m2) near-field light source. We succeeded in developing a large-area near-field light source that is densely constructed of uniform-size gold nanoparticles (AuNPs) two-dimensionally arrayed with regular interparticle gaps, which has tunable localized surface plasmon resonance bands (600–1100 nm). The near-field excitation properties based on the optical tunability of the AuNP two-dimensional arrays demonstrate that our chemical coating of large-area near-field light sources is widely applicable such as for high-sensitivity optical sensors and high-efficiency solar cells.
Lignin, an abundant terrestrial polymer, is the only large-volume renewable feedstock composed of an aromatic skeleton. Lignin has been used mostly as an energy source during paper production; however, recent interest in replacing fossil fuels with renewable resources has highlighted its potential value in providing aromatic chemicals. Highly selective degradation of lignin is pivotal for industrial production of paper, biofuels, chemicals, and materials. However, few studies have examined natural and synthetic molecular components recognizing the heterogeneous aromatic polymer. Here, we report the first identification of lignin-binding peptides possessing characteristic sequences using a phage display technique. The consensus sequence HFPSP was found in several lignin-binding peptides, and the outer amino acid sequence affected the binding affinity of the peptides. Substitution of phenylalanine7 with Ile in the lignin-binding peptide C416 (HFPSPIFQRHSH) decreased the affinity of the peptide for softwood lignin without changing its affinity for hardwood lignin, indicating that C416 recognised structural differences between the lignins. Circular dichroism spectroscopy demonstrated that this peptide adopted a highly flexible random coil structure, allowing key residues to be appropriately arranged in relation to the binding site in lignin. These results provide a useful platform for designing synthetic and biological catalysts selectively bind to lignin.
Solution-phase synchrotron X-ray absorption spectroscopy (XAS) is a powerful tool for structural and mechanistic investigations of paramagnetic organoiron intermediates in solution-phase reactions. For paramagnetic organotransition metal intermediates, difficulties are often encountered with conventional NMR-and EPR-based analyses. By using solution-phase XAS, we succeeded in identifying the organoiron species formed in the reaction of iron bisphosphine with mesitylmagnesium bromide, MesMgBr, and 1-bromodecane in a [FeX 2 (SciOPP)]-catalyzed KumadaTamaoCorriu (KTC)-type cross-coupling reaction. X-ray absorption near-edge structure (XANES) spectra showed that the resulting aryliron species possessed a divalent oxidation state. Extended X-ray absorption fine structure (EXAFS) demonstrated that the solution-phase molecular geometries of these species are in satisfactory agreement with the crystallographic geometries of [Fe The renaissance of iron-catalyzed cross-coupling reactions in the last decade 15 has been triggered by their unprecedented nonclassical reactivities and selectivities in comparison with conventional Pd and Ni catalysts.6 Recent worldwide interest in practical research applications, based on the utilization of abundant earth elements and the practical advantages of iron catalysts, including low cost, low toxicity, high availability, and easy separation of metal residues, have also demanded a much greater focus on iron-catalyzed cross-coupling reactions.
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