A high sensitive electrochemical nanostructure sensor based on graphene oxide/Fe3O4@SiO2 nanocomposite modified graphite screen printed electrode (GO/Fe3O4@SiO2/SPE) has been developed for trace analysis of acetaminophen. The electrochemical study of the modified electrode, as well as its efficiency for simultaneous voltammetric oxidation of acetaminophen and tryptophan is described. Compared w...

The chemical and sensing properties of porphyrins are frequently tuned via the introduction of peripheral substituents. In the context of the exceptionally fast second protonation step in the case of 5,10,15,20-tetraphenylporphyrin (TPP), as compared to porphin and 5,10,15,20-tetramesitylporphyrin (TMesP), we investigated the macrocycle-substituent interactions of these three porphyrin derivati...

The protonation of N2 bound to the active center of nitrogenase has been investigated using state-of-the-art density-functional theory calculations. Dinitrogen in the bridging mode is activated by forming two bonds to Fe sites, which results in a reduction of the energy for the first hydrogen transfer by 123 kJ/mol. The axial binding mode with open sulfur bridge is less reactive by 30 kJ/mol an...

The fluorescence properties of six different single Trp mutants of the mannitol-specific transporter of Escherichia coli were studied in order to derive structural information at different locations in the enzyme. The use of pure detergent and special protein purification protocols was essential for reliable fluorescence spectra, as judged from tyrosine-like fluorescence in a tryptophan-minus m...

We have measured the conductance of single peptides covalently bonded to two Au electrodes via S-Au bonds by repeatedly forming a large number of molecular junctions. The conductance decreases exponentially with the peptide length, with a decay constant of beta = 0.9 +/- 0.1 A-1, suggesting that tunneling is the mechanism of electron transport in the peptides. The conductance of the peptides is...

The incorporation of cadmium ions in porphyrins embedded in matrix monolayers is dominated by head group interactions as opposed to the effect of the average surface potential on interfacial cation concentrations. Similar phenomena are also observed in the adsorption of water-soluble porphyrin complexes to spread monolayers. The influence of such local interactions can be eliminated when the co...

This paper reports the synthesis of a 3-hydroxypropyl analog of HMPA. This ligand will be coordinated to SmI2, and kinetic studies are performed. This is worthy of study because the protonation step of the reduction mechanism, which typically occurs intermolecularly in SmI2-mediated reductions of carbonyls, will occur intramolecularly; thus, the potential exists for rate enhancement. The comple...

In this review we discuss the role of protonation states in receptor-ligand interactions, providing experimental evidences and computational predictions that complex formation may involve titratable groups with unusual pKa's and that protonation states frequently change from unbound to bound states. These protonation changes result in proton uptake/release, which in turn causes the pH-dependenc...

arthrobotrysamerospora (atcc 34468) produced glucoamylase in a semi-synthetic medium containing starch as a sole carbon source. polyacrylamide gel electrophoresis of crude glucoamylase showed three isoenzymes. they were designated as glu i, glu ii and glu iii according to their electrophoretic mobility. these iso-glucoamylases were purified by column chromatography using deae-sephadex a-50. the...