Non-Catalytic Benefits of Ni(II) Binding to an Si(111)-PNP Construct for Photoelectrochemical Hydrogen Evolution Reaction: Metal Ion Induced Flat Band Potential Modulation.

We report here the remarkable and non-catalytic beneficial effects of a Ni(II) ion binding to a Si|PNP type surface as a result of significant thermodynamic band bending induced by ligand attachment and Ni(II) binding. We unambiguously deconvolute the thermodynamic flat band potentials (VFB) from the kinetic onset potentials (Von) by synthesizing a specialized bis-PNP macrochelate that enables one-step Ni(II) binding to a p-Si(111) substrate. XPS analysis and rigorous control experiments confirm covalent attachment of the designed ligand and its resulting Ni(II) complex. Illuminated J-V measurements under catalytic conditions show that the Si|BisPNP-Ni substrate exhibits the most positive onset potential for the hydrogen evolution reaction (HER) (-0.55 V vs Fc/Fc+) compared to other substrates herein. Thermodynamic flat band potential measurements in the dark reveal that Si|BisPNP-Ni also exhibits the most positive VFB value (-0.02 V vs Fc/Fc+) by a wide margin. Electrochemical impedance spectroscopy data generated under illuminated, catalytic conditions demonstrate a surprising lack of correlation evident between Von and equivalent circuit element parameters commonly associated with HER. Overall, the resulting paradigm comprises a system wherein the extent of band bending induced by metal ion binding is the primary driver of photoelectrochemical (PEC)-HER benefits, while the kinetic (catalytic) effects of the PNP-Ni(II) are minimal. This suggests that dipole and band-edge engineering must be a primary design consideration (not secondary to catalyst) in semiconductor|catalyst hybrids for PEC-HER.

Characterization of isomeric allylic diols resulting from chlorophyll phytyl side-chain photo- and autoxidation by electron ionization gas chromatography/mass spectrometry.

The electron ionization (EI) mass spectral fragmentation of the trimethylsilyl derivatives of 3-methylidene-7,11,15-trimethylhexadecane-1,2-diol, Z- and E-3,7,11,15-tetramethylhexadec-3-ene-1,2-diols and Z- and E-3,7,11,15-tetramethylhexadec-2-ene-1,4-diols resulting from chlorophyll phytyl side-chain photo- and autoxidation was investigated. Different pathways (substantiated by deuterium labelling) were proposed in order to explain the main fragmentation observed. Then, some sufficiently specific fragment ions were selected and used to characterize these compounds in natural environmental samples.

Confirmation and quantitation of cocaine, benzoylecgonine, ecgonine methyl ester, and cocaethylene by gas chromatography/mass spectrometry. Use of microwave irradiation for rapid preparation of trimethylsilyl and T-butyldimethylsilyl derivatives.

The authors developed a technique by which cocaine metabolites as well as cocaethylene can be identified and quantitated using gas chromatography/mass spectrometry (GC/MS), and deuterated standards of benzoylecgonine, cocaine, ecgonine methyl ester, and cocaethylene as internal standards. The authors used a solid phase extraction (Clean Screen, Worldwide Monitoring Corporation, (Horsham, PA)) technique, and rapid derivatization of metabolites using microwave irradiation before GC/MS analysis. The t-butyldimethylsilyl derivatives (prepared by microwave irradiation in 2.5 minutes, 640 Watts [W]) offered better baseline separation and chromatography than conventional trimethylsilyl derivatives. The assay was linear between 0.87-17.3 mumol/L of benzoylecgonine (250-5,000 ng/mL) concentration, 0.83-16.6 mumol/L of cocaine (250-5,000 ng/mL), 0.79-15.8 mumol/L of cocaethylene (250-5,000 ng/mL) and 1.25-25.1 mumol/L of ecgonine methyl ester (250-5,000 ng/mL). The yields are comparable between the microwave technique and conventional heating.