Selective measurement of gaseous hydrogen peroxide with light emitting diode-based liquid-core waveguide absorbance detector.

Atmospheric H2O2 is typically determined by enzymatically mediated fluorogenic reactions that do not discriminate between H2O2 and organic peroxides. Reactions of Ti(IV) with H2O2 has also been the basis of colorimetric measurements of H2O2 but is too insensitive. A more sensitive determination is possible with the Ti(IV)-4-(2-pyridylazo)resorcinol (PAR) complex, however, unreacted PAR must be chromatographically separated. A titanium(IV)porphyrin complex, oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato]titanium(IV) [TiO(tpypH4)4+], (TiTPyP) was introduced for the measurement of aqueous H2O2. In this paper, we show that TiTPyP can be used for measuring H2O2(g)), it does not respond to CH3HO2. With a proper membrane collector, practically there is no interference from concurrently present gaseous SO2 and O3. The approach permits a S/N = 3 limit of detection (LOD) of 26 pptv with a 50 mm path liquid core waveguide (LCW) absorbance detector and a light emitting diode based light source. This is adequate for real atmospheric measurements.     

Hierarchical neural networks for the storage of correlated memories

A class of hierarchical neural network models introduced by Dotsenko for the storage and associative recall of strongly correlated memories is studied analytically and numerically. In these models, patterns stored in higher levels of the hierarchy represent generalized categories and those stored in lower levels describe finer details. We first show that the models originally proposed by Dotsenko have a serious flaw: they are not able to detect or correct errors in categorization which may be present in the input. We then describe three different models which attempt to overcome this shortcoming of the original models. In the first model, the interaction between different levels of the hierarchy has the form of an external field conjugate to memories stored in the lower level. In the second model, a three-spin interaction term is included in addition to the usual binary interactions of the Hopfield type. The third model makes use of a time delay mechanism to induce, if necessary, transitions between memory states and their complements. Detailed analytical and numerical studies of the performance of these models are presented. Our analysis shows that all three models are able to detect and also to correct in varying degrees any error in categorization that may be present in the input pattern.     

Determination of hydrogen peroxide by photoinduced fluorogenic reactions

4-Hydroxyproline, 8-hydroxyquinoline, 4-hydroxyquinoline-2-carboxylic acid and 4-hydroxyphenylacetic acid (HPA) react with H₂O₂ when irradiated with UV light to yield fluorescent products. Sub-micromolar detection limits of H₂O₂ are possible with HPA. The fluorescent product is the same as that formed in the peroxidase enzyme-mediated H₂O₂ oxidation of HPA. Several compounds that participate in the photomediated reaction do not react in the enzyme-mediated system. A mechanism for the photomediated reaction involving an aryloxy radical derived from the substrate is suggested. Although the limits of detection for H₂O₂ do not equal the best achievable with the enzyme-mediated systems, the simplicity of a single-step reaction and an ability to “photodevelop” the product offer a range of novel analytical possibilities.     

The reaction 2H(α,αp)n near threshold and excited states of 6Li

The reaction ²H(α,αp)n has been studied in a kinematically complete experiment between E_α=9.22 and 11.3 MeV (3.07 to 3.77 MeV in the CM system). Data at the highest energies are dominated by αp and αn final-state interactions and at the same time indicate the relevance of the broad state (J^π=2⁺, T=0) centered at 4.7 MeV in ⁶Li ignored heretofore in theoretical calculations. Possible effects due to three-body forces are discussed.     

Novel vanadium phosphate phases as catalysts for selective oxidation

In our effort to induce novel modifications in the structure of some important vanadium phosphate phases used as selective oxidation catalysts, it has been observed that metal ions such as Zn²⁺, Ni²⁺, Pd²⁺can be incorporated into the vanadyl hydrogen phosphate VOHPO₄0.5H₂O phase in very different ways depending upon the medium of preparation. It has been found that the metal ions are either substituted into the lattice with retention of structure of the parent compound or intercalated between the layers of a new mixed-valent phase. These new metal-incorporated phases are catalytically active and the palladium incorporated compound in particular displays shape selective catalysis for different oxidation and reduction reactions. In another approach, the preparation of VOHPO₄0.5H₂O) has been modified to give a novel crystalline phase containing mixed-valentvanadium and having NH₃ species bound to the lattice. This phase could be a potential catalyst for ammoxidation reactions. In addition, novel mesostructured vanadium phosphate phases have been prepared using a long-chain amine as the templating agent involving a ligand templating mechanism of formation.     

Characterisation of eco-friendly processing aids for rubber compound: Part II

According to the KEMI report, products with polycyclic aromatic compounds, PCA, levels exceeding 3% by weight must be labelled. The report pointed out that worn tyre tread material was being spread on the roadsides, introducing high amounts of PCA into the environment. PCA is having toxic effects on aquatic organisms. Polyaromatic-hydrocarbon-rich extender oils are to be banned by December 2009, which gives rise to challenges for the oil and rubber industries. In the present work, 10 types of naturally occurring oils and six types of petroleum-based oils were characterised in natural-rubber-based truck tyre tread cap compound. Compounds made with some of the naturally occurring oils showed better mechanical and dynamic mechanical properties.     

Use of a capacitance measurement device for surrogate noncontact conductance measurement

A capacitance to digital converter (AD7746) is used in the same mode as noncontact conductance detectors. The detector output is linearly proportional to specific conductance (sigma) at low sigma values but becomes nonlinear and reaches a plateau value at sigma approximately >0.75 mS/cm, regardless of the nature of the electrolyte. For all applications at sub- to low-mM concentrations, the device, available as an evaluation board, provides a very affordable nothing-else-required means of contactless surrogate conductivity detection from capillary scale to larger bore conduits. For the same measurement cell volume, the detector provides virtually the same limits of detection (LODs) as a standard galvanic contact conductivity detector in conventional scale suppressed conductometric ion chromatography. The detection limits deteriorate as the conduit inner diameter decreases.     

Real time HR-MAS NMR: application in reaction optimization, mechanism elucidation and kinetic analysis for heterogeneous reagent catalyzed small molecule chemistry

A novel application of in situ (1)H high-resolution magic angle spinning (HR-MAS) NMR technique for real-time monitoring of H(2)SO(4)-silica promoted formation of 2, 2-disubstituted quinozolin-4(3H)-ones is reported. The detailed NMR spectroscopic data led to elucidation of the mechanism, reaction optimization, kinetics and quantitative analysis of the product accurately and efficiently. The translation of the optimized parameters obtained by (1)H HR-MAS NMR in the wet laboratory provided similar results. It is proposed that (1)H HR-MAS has a potential utility for optimization of various organic transformations in solid supported catalyzed reactions.     

Energy transfer photophysics from serum albumins to sequestered 3-hydroxy-2-naphthoic acid, an excited state intramolecular proton-transfer probe

The steady-state and time-resolved studies of the sensitized emission of the excited-state proton transfer (ESIPT) probe 3-hydroxy-2-naphthoic acid (3HNA) when bound to bovine serum albumin (BSA) and human serum albumin (HSA) indicate that the nonradiative dipole-dipole F?rster type energy transfer from Trp singlet state of proteins to the ESIPT singlet state of 3HNA is greater in the case of HSA. This is supported by the distance and the orientation of the donor-acceptor pair obtained from the protein-ligand docking studies. The docking studies of the complex of BSA-3HNA also indicate that Trp 134 rather than Trp 213 is involved in the energy transfer process. The local environment of Trp 134 in BSA rather than that of Trp 213 is perturbed because of interaction with 3HNA as revealed by the optical resolution of Trp 134 phosphorescence in the complex at 77 K. Docking studies support the larger rotational correlation time, thetac (approximately 50 ns), observed for Trp residue/residues in the complexes of HSA and BSA compared with that in the free proteins.