Abstract:A palladium-mediated assembling strategy was developed to construct organized, three-dimensional multiporphyrin arrays, wherein layers of multiporphyrin arrays can be embedded via a Py-Pd-Py coordination unit directly on solid substrates. Multilayers of the multiporphyrin arrays were characterized by use of X-ray photoelectron, UV-vis, and fluorescence spectroscopy. A linear increase was observed for the absorption intensity of the Soret band of porphyrins or the π-π* charge transition with the layer numbers o… Show more
“…These curves revealed a broad absorption band between 200 and 500 nm, which could be attributed to the π−π* and n−π* electron transfer of the Pd− Py coordination unit, H 2 ase and MWNTs. 39 The absorption intensity at 290 nm was proportional with the layer numbers assembled (see the graph inserted in Figure 5), which indicated that similar amounts of the nanolinkers and Na 2 PdCl 4 connectors were assembled for each bilayer. A close inspection of the absorption increase could find a relatively larger increase for the coordination of the PdCl 4 2− ions, together with a smaller one for the coordination or adsorption of the bionanocomposites.…”
Section: ■ Results and Discussionmentioning
confidence: 88%
“…A possible reason may be that the PdCl 4 2− ions could coordinate with pyridine substituents more efficiently than those reported previously at the interfaces. 39 The assembling process was monitored by measuring the absorption spectra, XPS, FE-SEM, and AFM images as described below. Figure 5 shows the absorption spectra for the (Pd/MWNTPVPMe@H 2 ase) n LBL multilayers on the quartz surface after each assembly of the connector of Na 2 PdCl 4 and the nanolinker of MWNT-PVPMe@H 2 ase.…”
A metal-directed assembling approach has been developed to encapsulate hydrogenase (H2ase) within a layer-by-layer (LBL) multilayer of carbon nanotube polyelectrolyte (MWNT-PVPMe), which showed efficient biocatalytic oxidation of H2 gas. The MWNT-PVPMe was prepared via a diazonium process and addition reactions with poly(4-vinylpyridine) (PVP) and methyl iodide (MeI). The covalently attached polymers and organic substituents in the polyelectrolyte comprised 60-70% of the total weight. The polyelectrolyte was then used as a substrate for H2ase binding to produce MWNT-PVPMe@H2ase bionanocomposites. X-ray photoelectron spectra revealed that the bionanocomposites included the elements of Br, S, C, N, O, I, Fe, and Ni, which confirmed that they were composed of MWNT-PVPMe and H2ase. Field emission transmission electron microscope images revealed that the H2ase was adsorbed on the surface of MWNT-PVPMe with the domains ranging from 20 to 40 nm. Further, with the use of the bionanocomposites as nanolinkers and Na2PdCl4 as connectors, the (Pd/MWNT-PVPMe@H2ase)n multilayers were constructed on the quartz and gold substrate surfaces by the Pd(II)-directed LBL assembling technique. Finally, the as-prepared LBL multilayers were used as heterogeneous catalysts for hydrogen oxidation with methyl viologen (MV(2+)) as an electron carrier. The dynamic processes for the reversible color change between blue-colored MV(+) and colorless MV(2+) (catalyzed by the LBL multilayers) were video recorded, which confirmed that the H2ase encapsulated within the present LBL multilayers was of much stronger stability and higher biocatalytic activity of H2 oxidation resulting in potential applications for the development of H2 biosensors and fuel cells.
“…These curves revealed a broad absorption band between 200 and 500 nm, which could be attributed to the π−π* and n−π* electron transfer of the Pd− Py coordination unit, H 2 ase and MWNTs. 39 The absorption intensity at 290 nm was proportional with the layer numbers assembled (see the graph inserted in Figure 5), which indicated that similar amounts of the nanolinkers and Na 2 PdCl 4 connectors were assembled for each bilayer. A close inspection of the absorption increase could find a relatively larger increase for the coordination of the PdCl 4 2− ions, together with a smaller one for the coordination or adsorption of the bionanocomposites.…”
Section: ■ Results and Discussionmentioning
confidence: 88%
“…A possible reason may be that the PdCl 4 2− ions could coordinate with pyridine substituents more efficiently than those reported previously at the interfaces. 39 The assembling process was monitored by measuring the absorption spectra, XPS, FE-SEM, and AFM images as described below. Figure 5 shows the absorption spectra for the (Pd/MWNTPVPMe@H 2 ase) n LBL multilayers on the quartz surface after each assembly of the connector of Na 2 PdCl 4 and the nanolinker of MWNT-PVPMe@H 2 ase.…”
A metal-directed assembling approach has been developed to encapsulate hydrogenase (H2ase) within a layer-by-layer (LBL) multilayer of carbon nanotube polyelectrolyte (MWNT-PVPMe), which showed efficient biocatalytic oxidation of H2 gas. The MWNT-PVPMe was prepared via a diazonium process and addition reactions with poly(4-vinylpyridine) (PVP) and methyl iodide (MeI). The covalently attached polymers and organic substituents in the polyelectrolyte comprised 60-70% of the total weight. The polyelectrolyte was then used as a substrate for H2ase binding to produce MWNT-PVPMe@H2ase bionanocomposites. X-ray photoelectron spectra revealed that the bionanocomposites included the elements of Br, S, C, N, O, I, Fe, and Ni, which confirmed that they were composed of MWNT-PVPMe and H2ase. Field emission transmission electron microscope images revealed that the H2ase was adsorbed on the surface of MWNT-PVPMe with the domains ranging from 20 to 40 nm. Further, with the use of the bionanocomposites as nanolinkers and Na2PdCl4 as connectors, the (Pd/MWNT-PVPMe@H2ase)n multilayers were constructed on the quartz and gold substrate surfaces by the Pd(II)-directed LBL assembling technique. Finally, the as-prepared LBL multilayers were used as heterogeneous catalysts for hydrogen oxidation with methyl viologen (MV(2+)) as an electron carrier. The dynamic processes for the reversible color change between blue-colored MV(+) and colorless MV(2+) (catalyzed by the LBL multilayers) were video recorded, which confirmed that the H2ase encapsulated within the present LBL multilayers was of much stronger stability and higher biocatalytic activity of H2 oxidation resulting in potential applications for the development of H2 biosensors and fuel cells.
“…Other nanoscaled materials of porphyrins, such as tubes, rods, and crystals, can be formed from simple commercially available compounds or from more complex molecular designs. [18, 87] Self-assembled porphyrinic materials generally require specifically designed recognition motifs in predefined geometries to affect specific architectures. Conversely, the construction of self-organized materials, such as ONPs, does not require complex exocyclic moieties.…”
The catalytic oxidation of alkenes by most iron porphyrins using a variety of oxygen sources, but generally not dioxygen, yields the epoxide with minor quantities of other products. The turnover numbers for these catalysts are modest, ranging from a few hundred to a few thousand depending on the porphyrin structure, axial ligands, and other reaction conditions. Halogenation of substituents increases the activity of the metalloporphyrin catalyst and/or makes it more robust to oxidative degradation. Oxidation of cyclohexene by 5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl) (tppf 20 )] with a diameter of 10 nm, formed by host-guest solvent methods, catalytically oxidize cyclohexene with O 2 to yield only 2-cyclohexene-1-one and 2-cyclohexene-1-ol with approximately 10-fold greater turnover numbers compared to the non-aggregated metalloporphyrin in acetonitrile/methanol. These ONPs facilitate a greener reaction because the reaction solvent is 89% water and O 2 is the oxidant in place of synthetic oxygen sources. This reactivity is unexpected because the metalloporphyrins are in close proximity and oxidative degradation of the catalyst should be enhanced, thus causing a significant decrease in catalytic turnovers. The allylic products suggest a different oxidative mechanism compared to that of the solvated metalloporphyrins. These results illustrate the unique properties of some ONPs relative to the component molecules or those attached to supports.
“…174 Imahori and coworkers employed a supramolecular approach to organize porphyrin-fullerene doublecable structures (Scheme 65). 183 Alternating deposition of pyridylporphyrin 137 and K 2 PdCl 4 through pyridyl-to-Pd coordination, the method originally developed by Qian et al, 184 followed by incorporation of fullerene 138 through pyridylto-zinc coordination gave a surface-oriented double-cable structure on the SnO 2 electrode, that exhibited enhanced photobipolar properties. Employing specific interactions of proteins, straightforward supramolecular assemblies were obtained.…”
Section: A Supramolecular Organization On An Electrode Surfacementioning
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