Variety identification of wheat using mass spectrometry with neural networks and the influence of mass spectra processing prior to neural network analysis

The performance of matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry with neural networks in wheat variety classification is further evaluated.1 Two principal issues were studied: (a) the number of varieties that could be classified correctly; and (b) various means of pre-processing mass spectrometric data. The number of wheat varieties tested was increased from 10 to 30. The main pre-processing method investigated was based on Gaussian smoothing of the spectra, but other methods based on normalisation procedures and multiplicative scatter correction of data were also used. With the final method, it was possible to classify 30 wheat varieties with 87% correctly classified mass spectra and a correlation coefficient of 0.90.     

Analytical and preparative native polyacrylamide gel electrophoresis: Investigation of the recombinant and natural major grass pollen allergen Phl p 2

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot are amongst the most popular methods for allergen characterization, such as comparison of recombinant allergens with their natural counterparts. Native PAGE was evaluated as a possible robust and simple method offering high-resolution capacity for characterization of the major grass pollen allergen Phl p 2. Analytical separation of recombinant Phl p 2 provided a superior quality control in terms of homogeneity and, after Western blotting, immunoglobulin E (IgE) reactivity. Separation of natural Phl p 2 identified two major isoforms which were shown to have different N-terminal sequences and IgE-binding properties. After isolation using preparative native PAGE in combination with electrodialysis, both isoforms were investigated by specific proteolysis and reversed-phase high-performance liquid chromatography (RP-HPLC). The results demonstrate differences in the primary structures and that the recombinant counterpart corresponds exactly to one isoform. Analytical and preparative native PAGE thus proved to be powerful tools for the investigation of allergen isoforms and quality control of recombinant counterparts.     

Yields of Br* (4P ) as a function of wavelength in the photodissociation of Br2 and IBr

A flashlamp-pumped tunable dye laser has been used to study the photochemical production of Br* (4²P ) atoms from Br₂ and IBr exc     

Analysis of membrane protein cluster densities and sizes in situ by image correlation spectroscopy

Communication between cells invariably involves interactions of a signalling molecule with a receptor at the surface of the cell. Typically, the receptor is imbedded in the membrane and it is hypothesized that the binding of the signalling molecule causes a change in the state of aggregation of the receptor which, in turn, initiates a biochemical signal within the cell. Subsequently, many of the occupied receptors bind to membrane-associated structures, called coated pits, which invaginate and pinch off to form coated vesicles, thereby removing the receptors from the cell surface. The state of aggregation of membrane receptors is obviously in constant flux. Any useful approach to measuring the state of aggregation must, therefore, allow for dynamic measurements in living cells. It is possible to use fluorescently labelled signalling molecules or antibodies directed at the receptor of interest to visualize the receptor on the cell surface with a fluorescence microscope. By employing a laser confocal microscope, high resolution images can be produced in which the fluorescence intensity is quantitatively imaged as a function of position across the surface of the cell. Calculations of autocorrelation functions of these images provide direct and accurate measures of the density of fluorescent particles on the surface. Combined with the average intensity in the image, which reflects the total average number of molecules, it is possible to estimate the degree of aggregation of the receptor molecules. We refer to this analysis as image correlation spectroscopy (ICS). We show how ICS can be used to measure the density of several receptors on a variety of cells and how it can be used to measure the density of coated pits and the number of molecules per coated pit. We also show how the technique can be used to monitor fusion of virus particles to cell membranes. Further, we illustrate that, by calculating cross-correlation functions between pairs of images, we can extend the analysis to measurements of the distributions as a function of time, on the second timescale, as well as to measurements of the movement of the receptor aggregates on the surface. Finally, we illustrate that, by this approach, we can measure the extent of interaction between two different receptors as a function of time. This represents the most quantitative measurement of the extent of co-localization of receptors available and is independent of the spatial resolution of the confocal microscope. The theory of ICS and image cross-correlation spectroscopy (ICCS), focussing on the interpretation of the data in terms of the biological phenomenon being probed, is discussed.     

Diels-alder reactions with 2-(Arylsulfinyl)-1,4-benzoquinones: effect of aryl substitution on reactivity, chemoselectivity, and pi-facial diastereoselectivity

Diels-Alder reactions of (SS)-2-(2'-methoxynaphthylsulfinyl)-1, 4-benzoquinone (1b), 2-(p-methoxyphenylsulfinyl)-1,4-benzoquinone (1c), and 2-(p-nitrophenylsulfinyl)-1,4-benzoquinone (1d) with cyclopentadiene are reported. These cycloadditions allowed the highly chemo- and stereoselective formation of both diastereoisomeric endo-adducts resulting from reaction on the unsubstituted double bond C(5)-C(6) of quinones working under thermal and Eu(fod)(3)- or BF(3).OEt(2)-catalyzed conditions. The synthesis of endo-adduct [4aS,5S,8R,8aR,SS]-9d resulting from cycloaddition on the substituted C(2)-C(3) double bond was achieved in a chemo- and diastereoselective way from quinone 1d in the presence of ZnBr(2). The reactivity and selectivity of the process proved to be dependent on the electron density of the arylsulfinyl group.     

Double Asymmetric Synthesis and a New Strategy for Stereochemical Control in Organic Synthesis

This account examines double asymmetric induction from theoretical and practical viewpoints. In the context of four major organic reactions-the aldol, Diels-Alder, catalytic hydrogenation, and epoxidation-it is shown that a double asymmetric induction can be analyzed in terms of the single asymmetric reactions of each of the two chiral reactants. A rule which qualitatively relates the results of these single asymmetric reactions with the outcome of the double asymmetric reaction is proposed. A powerful new strategy based on this rule for the predictable creation of new chiral centers is discussed and the use of this strategy for the synthesis of sugars and macrolides is presented.     

Mössbauer study of119Sn defects in silicon from ion implantations of radioactive119In

Radioactive¹¹⁹In⁺ ions (T _1/2=2.1 min) obtained from the ISOLDE facility at CERN have been implanted into silicon single crystals at room temperature. Mössbauer emission spectra from the 24 keV -radiation of the daughter¹¹⁹Sn have been measured by fast resonance-counting technique. Five independent lines, characterized by their hyperfine parameters and Debye temperatures, have been found in the spectra. From the bonding configurations, deduced for the Sn impurity atoms, these are concluded to be located in four different defects in the silicon lattice. Simple models are proposed for the defects.     

Excess proton solvation and delocalization in a hydrophilic pocket of the proton conducting polymer membrane nafion

Solvation properties of the hydrated excess proton are studied in a hydrophilic pocket of Nafion 117 through a series of molecular dynamics simulations. The multistate empirical valence bond (MS-EVB) methodology, which enables the delocalization of the excess proton through the Grotthuss hopping mechanism, was employed for one of the excess protons in the simulation cell. Simulations were performed such that "classical" nondissociable hydronium cations and a single excess proton treated with the MS-EVB methodology were at a concentration ratio of 39:1. Two degrees of hydration of the Nafion polymer electrolyte membrane were simulated, each displaying the same marked difference between the solvation structures of the classical versus MS-EVB treated (Grotthuss shuttling) excess proton species. These differences are attributed to the solvent dynamics needed to transfer the cation between the solvent separated and contact pair positions about the sulfonic acid counterion. The results demonstrate that it is generally impossible to describe the low pH conditions in the hydrophilic domains of Nafion without the explicit treatment of Grotthuss delocalization in the underlying molecular dynamics model for the excess protons.     

Cascade radical cyclizations of benzannulated enyne-allenes. Unusual cleavage of a benzene ring leading to twisted 1,1'-dialkyl-9,9'-bifluorenylidenes and spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorenes

Treatment of the benzannulated enediynyl propargylic alcohol 16 (isomer ratio = 2:1) with thionyl chloride induced a sequence of reactions leading to the twisted 1,1'-dipropyl-9,9'-bifluorenylidene 17, the polycyclic compounds 18 and 19, and the spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 20 (trans/cis = 5:1). The transformation from 16 to the unexpected 17 presumably involved an initial formation of the benzannulated enyne-allene 21 followed by a C(2)-C(6) cyclization reaction and an intramolecular radical-radical coupling reaction, giving rise to the formal Diels-Alder adduct 23. Repeat of this sequence then furnished 24. Cleavage of the bond connecting the two carbons having the propyl substituent afforded 25. A subsequent rotation of the carbon-carbon bond joining the two central five-membered rings then gave the trans isomer 26. Oxidation of 26, presumably by oxygen, followed by hydrolysis then produced 17. Interestingly, the pathway leading to 17 involved an unusual cleavage of a benzene ring. The X-ray crystal structure of 17 reveals that it has a twist angle of 45.2 degrees for the carbon-carbon double bond connecting the two bifluorenylidene fragments. The spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 20 apparently was produced via two intramolecular [2 + 2] cycloaddition reactions of the benzannulated enyne-allene moieties, generated in situ from the benzannulated enediynyl propargylic alcohols. The twisted 1,1'-dimethyl-9,9'-bifluorenylidene 33 and the spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 39 (trans/cis = 3:1) were likewise produced from 32 and 38, respectively.     

Frequency measurements of far infrared cw lasing lines in optically pumped CHCl2F

The wavelengths, frequencies, and relative polarizations of 15 FIR cw lasing lines obtained by optically pumping CHCl₂F with a cw CO₂ laser have been measured. The lines are in the wavelength range from 340.3 to 905.4 m and were pumped by P- and R-branch laser lines in the 9 m band of CO₂.Supported in part by a joint grant with the U. S. National Science Foundation grant # INT80-19014 and the Brazilian Consellio Nacional de Pesquisas (CNPq)Contribution of the U. S. Government, not subject to copyright.