On-Chip Microdevice Unveils Reactant Enrichment Effect Dominated Electrocatalysis Activity in Molecular-Linked Catalysts.

Molecular functionalization has been intensely studied and artificially constructed to advance various electrocatalytic processes. While there is a widely approved charge-doping effect, the underlying action for reactant distribution/transport remains long neglected. Here an on-chip microdevice unravels that the proton enrichment effect at prototypical methylene blue (MB)/MoS2 interfaces rather than charge doping contributes to the hydrogen evolution reaction (HER) activity. Back-gated electrical/electrochemical tests detect quantitatively a strong charge injection from MB to MoS2 realized over diploid carrier density, but these excess carriers are unqualified for the actual enhanced HER activity (from 32 to 125 mA cm-2 at -0.29 V). On-chip electrochemical impedance further certifies that the proton enrichment in the vicinity of MoS2, which is generated by the nucleophilic group of MB, actually dominates the HER activity. This finding uncovers the leading function of molecular-linked catalysts.

Fluorescence quenching method for the determination of carbazochrome sodium sulfonate with aromatic amino acids.

In Britton-Robinson (BR) buffer medium (pH 3.3), carbazochrome sodium sulfonate (CSS) can react with some aromatic amino acids such as tryptophan (Trp), tyrosine (Tyr) and phenylalanine (Phe) to form a 1:1 complex by electrostatic attraction, aromatic stacking interaction and Van der Waals' force, resulting in fluorescence quenching of these amino acids. Maximum quenching wavelengths were located at 352 nm (CSS-Trp system), 303 nm (CSS-Tyr system) and 284 nm (CSS-Phe system), respectively. The fluorescence quenching value (ΔF) was proportional to the concentration of CSS in a certain range. The fluorescence quenching method for the determination of CSS showed high sensitivity, with detection limits of 31.3 ng/mL (CSS-Trp system), 44.6 ng/mL (CSS-Tyr system) and 315.0 ng/mL (CSS-Phe system), respectively. The optimum conditions of the reaction conditions and the effect of coexisting substances were investigated and results showed that the method had good selectivity. The method was successfully applied for the rapid determination of CSS in blood and urine samples. Based on the bimolecular quenching constant Kq , the effect of temperature and Stern-Volmer plots, this study showed that quenching of fluorescence of amino acids by CSS was a static quenching process.

Determination of carbazochrome by fluorescence quenching method.

A sensitive, simple and selective spectrofluorimetric method for the reaction of carbazochrome (CBZC) and Eosin Y (EY) or Phloxine B (PB) in acidic medium is developed for the determination of carbazochrome in biological fluids, which gives a highly fluorescent derivative measured at 545 and 565 nm at excitation wavelengths of 301 and 305 nm. The fluorescence quenching extent (ΔF) is proportional to the concentration of CBZC for CBZC-EY and CBZC-PB system at the range of 0.03-1.50 µg/mL and 0.08-1.25 µg/mL, respectively. The detection limit is 9.1 ng/mL for EY system and 22.7 ng/mL for PB system. The intra-day and inter-day reproducibility (RSD values) are less than 8.3% under three concentrations. Moreover, the affecting factors of fluorescence intensity of the product are carefully investigated and optimized, as well as the effect of coexisting substances. Judging from temperature, the Stern-Volmer plots and fluorescence emission decay curves, the quenching of fluorescence of EY and PB by CBZC is a static quenching process, caused by electrostatic attraction and aromatic stacking interaction.

Determination of tetracaine hydrochloride by fluorescence quenching method with some aromatic amino acids as probes.

A novel fluorescence quenching method for the determination of tetracaine hydrochloride (TA·HCl) concentration with some aromatic amino acids as fluorescence probe has been developed. In pH 6.3 acidic medium, tryptophane (Trp), tyrosine (Tyr) or phenylalanine (Phe) can react with tetracaine hydrochloride to form an ion-association complex by electrostatic attraction, aromatic stacking interaction and Van der Waals' force, which lead to fluorescence quenching of above amino acids. The maximum fluorescence excitation and emission wavelengths of them are located at 278, 274, 258 nm and 354, 306, 285 nm, respectively. The relative fluorescence intensity (F (0)/F) is proportional to the TA·HCl concentration in certain range. The linear ranges and detection limits are 1.2-5.0 µg/mL and 0.37 µg/mL for Tyr-TA·HCl system, 1.3-6.0 µg/mL and 0.38 µg/mL for Trp-TA·HCl system, and 1.4-6.0 µg/mL and 0.41 µg/mL for Phe-TA·HCl system. The optimum reaction conditions, influencing factors and the effect of coexisting substances are investigated. And the results show the method has a good selectivity. Judging from the effect of temperature, the Stern-Volmer plots and fluorescence lifetime determination, the quenching of fluorescence of amino acids by TA·HCl is a static quenching process.