Chromatographic detection using tris(2,2'-bipyridyl)ruthenium(III) as a fluorogenic electron-transfer reagent

Tris(2,2'-bipyridyl)ruthenium can be excited to fluorescence by visible light (lambda abs 454 nm, lambda em 607 nm) when in the M(II) oxidation state, but not in the M(III) state. A novel chromatographic detection method using the non-fluorescent M(III) form of the complex as a postcolumn fluorogenic reagent is demonstrated. The M(III) form is a powerful oxidizing agent (E degree = 1.27 V vs NHE, 1.05 V vs Ag/AgCl). The M(III) reagent is generated on-line from the M(II) form of the complex by a highly efficient porous carbon electrode and then reacted briefly with chromatographic effluent; the M(II) created by electron transfer from oxidation-susceptible analytes is then detected by fluorescence. The fluorescence detector can be calibrated for number of electrons transferred by injection of either M(II) or an oxidative standard such as ferrocyanide. It is hoped that this redox-based detection scheme will provide an alternative to electrochemical detection. Among the advantages are freedom from surface fouling and the potential for extremely low detection limits. The scheme was applied to detection of the peptide dynorphin A and several of its fragments. Dynorphin A contains tyrosine at the N-terminus (position 1) and tryptophan in position 15; these amino acid residues are susceptible to oxidation and peptides containing them can be detected on that basis. Flow injection testing of the model compounds Tyr-Gly-Gly-Phe-Leu and Gly-Gly-Trp-Gly indicated that tyrosine transferred approximately 1 electron to the M(III) reagent and that tryptophan transferred approximately 4 electrons. Similar results were obtained from the chromatographic runs. Dynorphin A and six dynorphin A fragments containing the N-terminal tyrosine were detected easily at 100 nM concentration (14 pmol) using laser-induced fluorescence. As expected, one fragment that did not contain tryptophan or tyrosine was not detected. A mass detection limit of 80 fmol was estimated for the tyrosine-containing fragments.     

Dynamical Emergence Theory (DET): A Computational Account of Phenomenal Consciousness

Minds and Machines - Scientific theories of consciousness identify its contents with the spatiotemporal structure of neural population activity. We follow up on this approach by stating and...     

Comparison of photophysical and colloidal properties of biocompatible semiconductor nanocrystals using fluorescence correlation spectroscopy

A number of different surface chemistries have been developed in recent years to render semiconductor nanocrystals (NCs) stable in water and biocompatible. However, most of these surface modifications affect NCs' photophysical properties, calling for a method to simultaneously monitor colloidal and fluorescence properties. Fluorescence correlation spectroscopy (FCS) combined with ensemble spectroscopic methods and Monte Carlo simulations were used to interpret and derive photophysical as well as colloidal properties of four different NC surface treatments. Using a novel FCS scheme with alternating laser excitation at two different intensities, we first ruled out influences from optical gradient forces (optical trapping). We then compared concentration of emitting particles, brightness per particle, saturation intensity, blinking (intermittency), hydrodynamic radius, and propensity for aggregation of the different bioconjugated NCs. This approach was successfully applied during the development and optimization of peptide-coated NCs.     

Effect of the long-term intake of an egg white hydrolysate on the oxidative status and blood lipid profile of spontaneously hypertensive rats

This paper examines the effects of the long-term consumption of egg white hydrolysed with pepsin (hEW) on the antioxidant status and lipid profile of spontaneously hypertensive rats (SHR). The antioxidant capacity was measured by the oxygen radical absorbance capacity (ORAC) and the oxidative status by the malon-dialdehyde (MDA) assay. The lipid profile was analysed spectrophotometrically. The radical-scavenging capacity of the plasma was increased and the MDA concentration in the aorta was decreased in the SHR treated with 0.5 g/kg/day of hEW. Our findings indicate that hEW played an important role in antioxidative defence of SHR and exerted a beneficial effect on the lipid profile, lowering triglycerides and total cholesterol without changing HDL levels. Therefore, hEW may be useful to prevent or reverse abnormalities associated with the metabolic syndrome and its complications, such as hypertension, oxidative stress and hyperlipidemia.     

Modeling nitrate fluxes at the catchment scale using the integrated tool CAWAQS

Nitrates fluxes in the Grand Morin basin (1200 km(2)), that is subjected to intense agricultural pressure, are considered using in-stream observations (around 250 sampling days over 5 years) and physically based simulations using the CAWAQS model (CAtchment WAter Quality Simulator). In-stream nitrate concentration averaged 6 mg N L(-1), increasing by approximately 0.2 mg N L(-1) yr(-1) around this value (period 1991-1996). Our results show that, over the period of 1991-1996, the differences between in-stream observed nitrate concentrations and simulated nitrate concentrations result from nitrate losses at the basin scale. These losses are due to denitrification by transfer through wetlands, alluvial plains, the hyporheic zone, and by benthic processes in rivers. A mean annual mass balance at the basin scale indicates that 40% of the infiltration flux (3360 kg N km(-2) yr(-1)) is removed from the system via the river network, 40% is stored in aquifers and 20% is lost by denitrification (period 1991-1996).     

Metal and semi-metal precipitates in Nuclepore membranes

Au, Pt, Ag, Sb, Te, In and Ge were precipitated by a salt-reducing agent reaction into the pores of Nuclepore membranes 10 to 600 nm pore size range. The precipitates form filament-like structures inside the pores and a dendritic growth on the surface. The permeation of water as a function of pore size in the Nuclepore membranes was measured by tracing the diffusion through the membrane with tritium. The results are modelled and theoretical predictions are compared with the experimentally observed kinetics for metal deposition in the membranes. Also the d.c. electrical properties of the metal precipitates were measured. The anisotropic electrical properties of these systems are dictated by the morphology of the precipitated metal on the membrane.     

Research Needs and Challenges in Application of Computer and Information Sciences for Industrial Engineering

By invitation from the Editor of IIE Transactions, a research forum was established in 1987 to develop and prepare this article. The objective: to write on the directions, needs and challenges for research by the IE com-munity in applying computer and information sciences. The motivation: realizing the major advancements in computer and information sciences in the recent decade and their significant impact on the IE profession, it is vital to examine how IE research activities can respond effectively to current and emerging needs. This article is viewed as a useful contribution to such an examination.

Forum members were invited from academia, government and industry based on their experience in and commitment to research in this area. The forum was chaired by Shimon Y. Nof and the members are the co-authors of this article.

Forum members communicated and deliberated throughout 1987 and met for a review and planning session dur-ing the IIE Conference in Washington, D.C. in May, 1987 (Forum, 1987). The following article summarizes the contributions and recommendations of the forum members, and was reviewed by four guest reviewers. The re-viewers, invited by the Editor, have provided comments that have been incorporated into this article     

A Low-Pressure Excimer Light Source for a Spectral Region of 170–310 nm

A low-pressure excimer light source pumped by a longitudinal dc glow discharge operates on the B–X and D–X transitions of Ar, Kr, and Xe chlorides and on the D–A transition of chlorine molecules. The output characteristics of a source with a discharge region 100 mm long and an inner diameter of the discharge tube of 5 mm were optimized on Xe(Kr, Ar)/Cl₂, Ar/Kr/Cl₂, Ar/Xe/Cl₂, and Kr/Xe/Cl₂ mixtures. The light source operated within a spectral range of 170 to 310 nm. The average radiation power and operation efficiency were 1.8–8.2 W and 21%, respectively.