Multi-analyte sensing: a chemometrics approach to understanding the merits of electrode arrays versus single electrodes

A peptide-modified electrode array with a different peptide on each electrode is compared with a single electrode modified with many peptides for the voltammetric measurement of concentrations of Cu(2+), Cd(2+) and Pb(2+) in solution. The single gold electrode was modified simultaneously with peptides Gly-Gly-His, glutathione and angiotensin I each coupled to thioctic acid, and thioctic acid itself, and the calibration of mixtures of ions was compared with previously published data from an array of four sensors each with an individual modification. Calibration at the multi-peptide single-electrode sensor was by two-way partial least squares (voltammetric current measured with variables 'sample' x 'potential') and for the electrode array by three-way NPLS1 ('sample' x 'potential' x 'electrode'). The advantage of designing experiments to yield multi-way data is demonstrated and discussed.     

N-heterocycle chelated oxomolybdenum(VI and V) complexes with bidentate citrate

A 1,10-phenanthroline (phen) chelated molybdenum(VI) citrate, [(MoO2)2O(H2cit)(phen)(H2O)2] x H2O (1) (H4cit = citric acid), is isolated from the reaction of citric acid, ammonium molybdate and phen in acidic media (pH 0.5-1.0). A citrato oxomolybdenum(V) complex, [(MoO)2O(H2cit)2(bpy)2] x 4H2O (2), is synthesized by the reduction of citrato molybdate with hydrazine hydrochloride in the presence of 2,2'-bipyridine (bpy), and a monomeric molybdenum(VI) citrate [MoO2(H2cit)(bpy)] x H2O (6) is also isolated and characterized structurally. The citrate ligand in the three neutral compounds uses the alpha-alkoxy and alpha-carboxy groups to chelate as a bidentate leaving the two beta-carboxylic acid groups free, that is different from the tridentate chelated mode in the citrato molybdate(VI and V) complexes. 1 and in solution show obvious dissociation based on 13C NMR studies.     

Engineering inorganic hybrid nanoparticles: tuning combination fashions of gold, platinum, and iron oxide

Multistep colloidal chemical routes were employed to synthesize Pt/Au, Pt/iron oxide (IO), and Au/Pt/IO hybrid nanoparticles (NPs). The starting templates, Pt NPs, were synthesized by controlling the decomposition kinetics of platinum acetylacetonate in oleylamine. The morphologies of binary metal Pt/Au hybrid NPs were modulated by controllable attachment of Au nanoscale domains to Pt templates. Similarly, Pt/IO and Au/Pt/IO hybrid NPs were fabricated by the controllable attachment of Fe to the Pt or Pt/Au template NPs. The noble metal domains of as-prepared hybrid NPs had face center cubic crystal structures and did not alloy, as verified by high resolution transmission electron microscopy and X-ray diffraction spectrometry. X-ray diffraction spectrometry study indicates that the IO domains in the as-prepared NPs have a spinel structure. UV-vis study of binary metal Pt/Au hybrid NPs revealed that they have a characteristic plasmon resonance around 525 nm, while dumbbell-like Au/Pt/IO NPs had a plasmon resonance around 600 nm. Furthermore, magnetism study of the binary Pt-IO NPs clearly indicated that the interfacial interactions between Pt and IO domains could result in a shift of the blocking temperature.     

Tuning excited-state electron transfer from an adiabatic to nonadiabatic type in donor-bridge-acceptor systems and the associated energy-transfer process

Through design and synthesis of a new series of dyads I-III composed of 2,3-dimethoxynaphthalene as an electron donor (D) and 2,3-dicyanonaphthalene as an acceptor (A) bridged by n-norbornadiene (n = 1-3) we demonstrate an excellent prototype to switch the excited-state electron-transfer dynamics from an adiabatic to a nonadiabatic process. I reveals a remarkable excitonic effect and undergoes an adiabatic type of electron transfer (ET), resulting in a unique charge-transfer emission, of which the peak wavelength exhibits strong solvatochromism. Conversely, upon exciting the donor moiety, a fast D --> A energy transfer takes place for II (approximately 3 ps) and III (< or =30 ps), followed by a nonadiabatic type, weak coupled electron transfer with a relatively slow ET rate, giving rise to dual emission in polar solvents. Further detailed temperature-dependent studies of the ET rate deduced reaction barriers of 2.7 kcal/mol (for II) and 1.3 kcal/mol (for III) in diethyl ether and CH2Cl2, respectively. The results lead to a deduction of the reaction free energy and reorganization energy for both II (in diethyl ether) and III (in CH2Cl2). Theoretical (for I) and experimental (for II and III) approaches estimate the electronic coupling to be 860, 21.9, and 3.2 cm(-1) for I, II, and III, respectively, supporting the adiabatic versus nonadiabatic switching mechanism.