Hydrogen production in the radiolysis of bromide solutions

The radiolysis of water without a protecting agent is found to form a low steady-state concentration of molecular hydrogen. The addition of bromide anion leads to a linear response for molecular hydrogen production with doses up to 300 kGy. Bromide concentrations are found to remain constant over this dose range due to recycling of the oxidized species containing the bromine atom by hydrated electrons, H atoms or HO₂ (O₂⁻). This process appears to occur many times with little change in total bromide anion concentration. Efficient electron scavengers are found to have no effect on bromide anion concentration except possibly at extremely high concentrations. Nitrous oxide saturated solutions show a significant depletion of bromide anion concentration with a concurrent formation of BrO₃⁻ and a suppressed yield of molecular hydrogen.     

A grasp-knapsack hybrid for a nurse-scheduling problem

This paper is concerned with the application of a GRASP approach to a nurse-scheduling problem in which the objective is to optimise a set of preferences subject to a set of binding constraints. The balance between feasibility and optimality is a key issue. This is addressed by using a knapsack model to ensure that the solutions produced by the construction heuristic are easy to repair. Several construction heuristics and neighbourhoods are compared empirically. The best combination is further enhanced by a diversification strategy and a dynamic evaluation criterion. Tests show that it outperforms previously published approaches and finds optimal solutions quickly and consistently.     

Purely heterometallic lanthanide(III) macrocycles through controlled assembly of disulfide bonds for dual color emission

Lanthanide complexes based on bis(amides) of diethylenetriaminepentaacetic acid with thiol functionalities are modified with 2,2'-dipyridyl disulfide to give activated complexes that can selectively react with thiol-functionalized complexes to form heterometallic lanthanide macrocycles. The preparation and full characterization of the polyaminocarboxylate ligands N,N'-bis[p-thiophenyl(aminocarbonyl)]diethylenetriamine-N,N',N'-triacetic acid (H(3)L(x)) and the activated N,N'-bis[p-(pyridyldithio)[phenyl(aminocarbonyl)]]diethylenetriamine-N,N',N'-triacetic acid (H(3)L(y)) and the complexes LaL(x), NdL(x), SmL(x), EuL(x), GdL(x), DyL(x), TbL(x), ErL(x), and YbL(x) are reported. The luminescence properties of the LnL(x) complexes emitting in the visible (where Ln = Dy(3+), Tb(3+), Eu(3+), and Sm(3+)) are examined by steady-state and time-resolved photoluminescence, and the triplet state energy level of GdL(x) was estimated to be 24?100 cm(-1) from the 0-0 band of the 77 K phosphorescence spectrum. Near-infrared emission was detected for the NdL(x), YbL(x), and ErL(x) complexes, demonstrating the versatility of the thiophenol chromophore. The assembly of purely heterometallic EuTbL(x)(2) macrocycles by reaction of EuL(x) with TbL(y) was followed by UV-vis absorption spectroscopy, monitoring the characteristic absorption peak of pyridyl-2-thione at 353 nm. Analysis of the solution by mass spectrometry reveals the formation of purely heterometallic macrocycle EuTbL(x)(2). This is in contrast with the results obtained by dynamic self-assembly under oxidative conditions, where we observe a statistical mixture of macrocyclic complexes of Eu(2)L(x)(2), Tb(2)L(x)(2), and EuTbL(x)(2). The EuTbL(x)(2) macrocycle displays dual color emission, incorporating the characteristic f-f transitions of Eu(3+) and Tb(3+). Investigation into the time-resolved photophysical properties of EuTbL(x)(2) reveals energy transfer from Tb(3+) to Eu(3+), facilitated by the different conformations of the macrocycle in solution.     

Correlation between molecular conformation, packing, and dynamics in oligofluorenes: a theoretical/experimental study

Fluorene-based systems have shown great potential as components in organic electronics and optoelectronics (organic photovoltaics, OPVs, organic light emitting diodes, OLEDs, and organic transistors, OTFTs). These systems have drawn attention primarily because they exhibit strong blue emission associated with relatively good thermal stability. It is well-known that the electronic properties of polymers are directly related to the molecular conformations and chain packing of polymers. Here, we used three oligofluorenes (trimer, pentamer, and heptamer) as model systems to theoretically investigate the conformational properties of fluorene molecules, starting with the identification of preferred conformations. The hybrid exchange-correlation functional, OPBE, and ZINDO/S-CI showed that each oligomer exhibits a tendency to adopt a specific chain arrangement, which could be distinguished by comparing their UV/vis electronic absorption and (13)C NMR spectra. This feature was used to identify the preferred conformation of the oligomer chains in chloroform-cast films by comparing experimental and theoretical UV/vis and (13)C NMR spectra. Moreover, the oligomer chain packing and dynamics in the films were studied by DSC and several solid-state NMR techniques, which indicated that the phase behavior of the films may be influenced by the tendency that each oligomeric chain has to adopt a given conformation.     

Analytical approaches to determination of total choline in foods and dietary supplements

Choline is a quaternary amine that is synthesized in the body or consumed through the diet. Choline is critical for cell membrane structure and function and in synthesis of the neurotransmitter acetylcholine. Although the human body produces this micronutrient, dietary supplementation of choline is necessary for good health. The major challenge in the analysis of choline in foods and dietary supplements is in the extraction and/or hydrolysis approach. In many products, choline is present as choline esters, which can be quantitated individually or treated with acid, base, or enzymes in order to release choline ions for analysis. A critical review of approaches based on extraction and quantitation of each choline ester as well as hydrolysis-based methods for determination of total choline in foods and dietary supplements is presented.     

Forensic analysis of <Emphasis Type="Italic">Salvia divinorum</Emphasis> using multivariate statistical procedures. Part I: discrimination from related <Emphasis Type="Italic">Salvia</Emphasis> species

Salvia divinorum is a hallucinogenic herb that is internationally regulated. In this study, salvinorin A, the active compound in S. divinorum, was extracted from S. divinorum plant leaves using a 5-min extraction with dichloromethane. Four additional Salvia species (Salvia officinalis, Salvia guaranitica, Salvia splendens, and Salvia nemorosa) were extracted using this procedure, and all extracts were analyzed by gas chromatography–mass spectrometry. Differentiation of S. divinorum from other Salvia species was successful based on visual assessment of the resulting chromatograms. To provide a more objective comparison, the total ion chromatograms (TICs) were subjected to principal components analysis (PCA). Prior to PCA, the TICs were subjected to a series of data pretreatment procedures to minimize non-chemical sources of variance in the data set. Successful discrimination of S. divinorum from the other four Salvia species was possible based on visual assessment of the PCA scores plot. To provide a numerical assessment of the discrimination, a series of statistical procedures such as Euclidean distance measurement, hierarchical cluster analysis, Student’s t tests, Wilcoxon rank-sum tests, and Pearson product moment correlation were also applied to the PCA scores. The statistical procedures were then compared to determine the advantages and disadvantages for forensic applications.     

Gold nanoparticle chemiresistors operating in biological fluids

Functionalised gold nanoparticle (Au(NP)) chemiresistors are investigated for direct sensing of small organic molecules in biological fluids. The principle reason that Au(NP) chemiresistors, and many other sensing devices, have limited operation in biological fluids is due to protein and lipid fouling deactivating the sensing mechanism. In order to extend the capability of such chemiresistor sensors to operate directly in biofluids, it is essential to minimise undesirable matrix effects due to protein and lipidic components. Ultrafiltration membranes were investigated as semi-permeable size-selective barriers to prevent large biomolecule interactions with Au(NP) chemiresistors operating in protein-loaded biofluids. All of the ultrafiltration membranes protected the Au(NP) chemiresistors from fouling by the globular biomolecules, with the 10 kDa molecular weight cut-off size being optimum for operation in biofluids. Titrations of toluene in different protein-loaded fluids indicated that small molecule detection was possible. A sensor array consisting of six different thiolate-functionalised Au(NP) chemiresistors protected with a size-selective ultrafiltration membrane successfully identified, and discriminated the spoilage of pasteurised bovine milk. This proof-of-principle study demonstrates the on-chip protein separation and small metabolite detection capability, illustrating the potential for this technology in the field of microbial metabolomics. Overall, these results demonstrate that a sensor array can be protected from protein fouling with the use of a membrane, significantly increasing the possible application areas of Au(NP) chemiresistors ranging from the food industry to health services.     

Microfluidic system for simultaneous optical measurement of platelet aggregation at multiple shear rates in whole blood

Thrombosis is the pathological formation of platelet aggregates which occlude blood flow causing stroke and heart attack-the leading causes of death in developed nations. Instrumentation for diagnosing and exploring treatments for pathological platelet aggregation thus has the potential for major clinical impact. Most current thrombosis methods focus on single flow conditions, non-occlusive platelet adhesion, or low shear rates and so are limited in their application to comparative studies involving multiple, pathological test conditions (e.g., shear rate, stenotic geometries that mimic arteries, and rapid platelet accumulation to occlusion). The field could benefit from a low volume, high throughput, short analysis time, and low cost system while minimizing sample handling. We report on the design, fabrication, testing, and application of a microfluidic device and associated optical system for simultaneous measurement of platelet aggregation at multiple initial shear rates within four stenotic channels in label-free whole blood. Following computational design, requisite shear rates were achieved in the device by micro- surface milling a mold and subsequent PDMS casting. We applied the microfluidic system to measure platelet aggregation in whole porcine blood for shear rates spanning physiological to pathological flow conditions (500-13000 s(-1)). Real-time, non-contact, label-free, microscope-free measurements of platelet aggregation were acquired using an optical system comprising a 650 nm diode laser and a linear CCD. We observed fully occlusive platelet aggregation in less than 20 min above a threshold initial shear rate of 4000 s(-1), and no occlusive platelet aggregation below 1500 s(-1) (N = 86 trials). Accumulation of thrombus was consistent between laser intensity, light microscopy, histology, and mass flow rate measurements. The amount of blood volumes producing occlusion were dependent on shear rate. Times to occlusion were not found to be dependent on shear rate above the threshold level of 4000 s(-1). This microfluidic system enables measurement of the entire process of occlusive platelet thrombosis in whole, unlabeled blood, in vitro, at multiple shear rates. Such a system may be useful as a point-of-care diagnostic tool for studying anti-platelet therapies in individual blood samples from high-risk patients.     

Nocardiopsins: New FKBP12‐Binding Macrolide Polyketides from an Australian Marine‐Derived Actinomycete,Nocardiopsis sp.

A marine‐derived actinomycete, Nocardiopsis sp. (CMB‐M0232), obtained from a sediment sample collected at a depth of 55 m off the coast of Brisbane, Australia, yielded two new macrolide polyketides. Structures for nocardiopsins A and B were assigned by detailed spectroscopic analysis, degradation and chemical derivatization. A Marfey’s analysis revealed an unexpected acid‐mediated partial racemization of the L ‐pipecolic acid incorporated within the nocardiopsins. The scope of this racemization was assessed against a selection of natural and synthetic N‐acyl pipecolic acids. While the nocardiopsins are not antibacterial, antifungal or cytotoxic, they do exhibit low‐micromolar binding to the immunophilin FKBP12, consistent with their structural and biosynthetic relationship to the immunosuppressive agents FK506 and rapamycin. The nocardiopsins represent a new point of entry into what has been a valuable, exclusive and reclusive region of bioactive chemical space—that surrounding the FK506/rapamycin pharmacophore.     

Analysis of Basic Drugs: A Comparison of Two Different Strong Cation Exchange-Modified LC Packings

Evidence in the literature of systematic investigation of retention mechanisms on strong cation-exchange (SCX) modified silica LC packings is lacking. In this study, the retention behaviour of selected basic drugs using a propylbenzenesulfonic acid-modified packing (Nucleosil 100SA) were compared, under similar conditions, with previous findings from a propylsulfonic acid-modified packing (Waters Spherisorb S5SCX). Eluent ionic strength, apparent pH, and solvent composition were investigated. Good efficiency (70,000 plates m^?1) and peak symmetry (<1.5) were observed using the Nucleosil 100SA packing. The use of different alkyl ‘spacer’ moieties in each packing influenced retention, with hydrophobic partitioning of analytes more evident for the Nucleosil packing compared with Spherisorb, particularly when water-containing eluents were used. On Nucleosil 100SA, non ion-exchange interactions accounted for up to 61% of retention. Despite some correlation with analyte LogP on Nucleosil 100SA, and the environment surrounding basic nitrogen moieties, retention on both SCX packings was unrelated to analyte pK _a.