In a comparative study of the electrocatalytic CO2 reduction, cobalt meso-tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the former case, employing N,N-dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO2 becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO2. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone. 相似文献
Recently, 1,1′‐bi‐2‐naphthol (BINOL)‐based N‐triflylphosphoramides emerged as a new class of potent Brønsted acid catalysts. In this paper we describe the efficient synthesis of various BINOL‐based N‐triflylphosphoramides and their calcium salts. Furthermore, X‐ray crystal structure analysis combined with energy‐dispersive X‐ray spectroscopy (EDX) measurements confirmed that the synthesised chiral N‐triflylphosphoramides are highly acidic metal‐free catalysts. 相似文献
S‐Layer proteins are an example of bionanostructures that can be exploited in nanofabrication. In addition to their ordered structure, the ability to self‐assembly is a key feature that makes them a promising technological tool. Here, in vitro self‐assembly kinetics of SpbA was investigated, and found that it occurs at a rate that is dependent on temperature, its concentration, and the concentration of calcium ions and sodium chloride. The activation enthalpy (120.81 kJ · mol?1) and entropy (129.34 J · mol?1 · K?1) obtained infers that the incorporation of monomers incurs in a net loss of hydrophobic surface. By understanding how the protein monomers drive the self‐assembly at different conditions, the rational optimization of this process was feasible.
Synthetic imidazole ligands are typically substituted at the N(1) ((1)-Im) position while natural imidazole ligands are substituted at the C(4) ((4)-Im) position. To outline the difference in coordination properties, the methyl-substituted imidazoles Me(4)-Im and Me(1)-Im were complexed with CuCl(2) and ZnCl(2) and investigated by NMR relaxometry, electron paramagnetic resonance, far-Fourier transform IR vibrational spectroscopy, and ab initio calculations. Me(4)-Im, Me(1)-Im, and Im in excess form the usual tetragonal D(4h) [CuL(4)X(2)] complexes with CuCl(2) whereas the methylated imidazoles form pseudotetrahedral C(2v) complexes instead of the usual octahedral O(h) [ZnIm(6)](2+) complex. All imidazoles display a high degree of covalence in the M-L σ- and π-bonds and the π-interaction strength affects the relative energies of complexation. Opportunities to tailor complexes by the chemical properties of the substituents are envisaged due to the role of the inductive and hyperconjugative effects, rather than position. 相似文献
Porous layer open tubular (PLOT) polystyrene divinylbenzene columns have been used for separating intact proteins with gradient elution. The 10 μm I.D. × 3 m columns were easily coupled to standard liquid chromatography–mass spectrometry (LC–MS) instrumentation with commercially available fittings. Standard proteins separated on PLOT columns appeared as narrow and symmetrical peaks with good resolution. Average peak width increased linearly with gradient time (tG) from 0.14 to 0.33 min (tG 20 and 120 min, respectively) using a 3 m column. With shorter columns, peak widths were larger and increased more steeply with gradient time. Theoretical peak capacity (nc) increased with column length (tested up to 3 m). The nc increased with tG until a plateau was reached. The highest peak capacity achieved (nc = 185) was obtained with a 3 m column, where a plateau was reached with tG 90 min. The within- and between column retention time repeatabilities were below 0.6% and below 2.5% (relative standard deviation, RSD), respectively. The carry-over following injection of 0.5 ng per protein was less than 1.1%. The retention time dependence on column temperature was investigated in the range 20–50 °C. Proteins in a skimmed milk sample were separated using the method. 相似文献