Charles E. Cottrell

Effect of signal-to-noise radio and number of data points upon precision in measurement of peak amplitude, position and width in Fourier transform spectrometry

Abstract Chen, L., Cottrell, C.E. and Marshall, A.G., 1986. Effect of signal-to-noise ratio and number of data points upon precision in measurement of peak amplitude, position and width in Fourier transform spectrometry. Chemometrics and Intelligent Laboratory Systems , 1: 51–58. The theoretical precision in determining experimental spectral peak parameters (height, width, and position) should depend in a calculable way upon the peak shape, signal-to-noise ratio, and number of data points per line width. Expressions for precision in peak position and width for absorption-mode Lorentzian and Gaussian line shapes have been derived previously. We have extended the theory to include absorption-mode sinc as well as magnitude-mode Lorentzian and sinc line shapes, and have computed the predicted precision in peak amplitude as well as in position and width. Experimental (Fourier transform ion cyclotron resonance mass spectrometry and Fourier transform nuclear magnetic resonance spectrometry) precision for each of these parameters is found to be significantly poorer (e.g., factor of 5) than the theoretical predictions. The present results provide a direct test of the nature of noise (e.g., vertical vs. horizontal) in Fourier transform spectra, and suggest that experimental measurements of Fourier transform spectral line shape parameters may be much less precise than previously suspected.

An inexpensive, versatile sample illuminator for photo-CIDNP on any NMR spectrometer

Photochemically induced dynamic nuclear polarization (photo-CIDNP) of proteins requires the introduction of ca. l-7 W of 488 nm light directly into NMR samples (1). This has been previously accomplished by a number of configurations: directing the light beam via an optical bench and mirrors through the bottom of the supercon NMR probe to a flat-bottom NMR sample tube; or, alternatively, focusing the light through a cylindrical quartz rod with a 45” polished end to convey a diverged light beam to the side of a spinning sample tube in the rf coil (2). In both cases, costly probe modifications are necessary, including removal or alteration of the variable temperature control apparatus. Laser beam alignment (into a mirror at the magnet base) can also be awkward and time consuming. Lerman and Cohn (3) illuminated samples by inserting a coupled optical fiber directly into the NMR sample solution. Kaptein and Dykstra (personal communication) have fixed a prism at the end of an optical fiber and situated it between the rf coil windings of a modified Bruker 360 MHz proton probe. We report here an alternative modification utilizing fiber optics illumination. Coupling to the laser was accomplished with a Newport Corporation (Fountain Valley, Calif.) model F-LFI-CO-25 (

Dasytrichone, A Novel Flavone From Dasymaschalon Trichophorum With Cancer Chemopreventive Potential

850.00) fiber optics coupler laser head mount (universally mounts to any laser bezel mount) with 25 ft of 200 p fiber in place of the standard 10 ft length and armored handpiece. The free output end was stripped free of cladding (l-2 cm length) and inserted into a 2 mm stem coaxial insert (Cat. No. 5203, Wilmad Glass Company, Inc., Buena, N.J.) which fits snuggly into a 5 mm sample tube (Fig. 1). Maximal illumination was observed when the fiber tip was positioned in the center of the rf coil region. The laser light probe was introduced by triggering an inexpensive solenoid mounted to the coupling head slide shutter under computer control. Light coupling was fine tuned with x, y, and z adjustments on the coupling head. For maximal efficiency the fiber must be cut perfectly flat and well polished. Coupling efficiencies of up to 90% were typically measured. In a nonspinning sample of 1 mA4 tyrosine (pH 7.0) and 0.4 r&4 ‘?N-carboxyethyllumiflavin, the tyrosyl 3,5 protons were enhanced (light intensity-dark intensity)/ (dark intensity) 1Zfold at 500 MHz on an NTC spectrometer with a Spectra Physics 165-9 argon ion laser operating at 7.0 W (all lines). Figure 2 displays the light-dark

On the conformation of UDP-Glc, a sugar nucleotide

Abstract Dasytrichone, A Novel Flavone With An Unusual A-Ring Substitution Pattern Was Isolated From The Stems And Leaves Of Dasymaschalon Trichophorum Merr. (Family Annonaceae). Its Structure Was Established By Spectroscopic Methods And Single Crystal X-Ray Crystallography. Dasytrichone Inhibits The Metabolism Of The Carcinogen Benzo[A]Pyrene By Hamster Embryo Cell Cultures, Suggesting That It Warrants Further Evaluation As A Potential Chemopreventive Agent.

Procedure for processing spectroscopic dispersion vs absorption (DISPA) line shapes

UDP-Glc [uridine 5′- (α-D-glucopyranosyl pyrophosphate)] is present in a folded conformation, at least in part, in a number of solvents and in vacuo based on differential reactivity studies of its hydroxy groups, NOE effects, and ab initio calculations.

15N resonance assignments of oxidized and reducedChromatium vinosum high-potential iron protein

Abstract For a single Lorentzian line, a plot of dispersion versus absorption (DISPA) gives a perfect circle. For any line shape, the magnitude and direction of displacement of an experimental DISPA plot from its reference circle can be used to diagnose the line-broadening mechanism (e.g. multiple peak positions, multiple peak widths, chemical exchange, saturation broadening, etc.), based on the digitized envelope of a single spectrum. The present algorithm generates normalized absorption and dispersion data sets curves from digitized experimental spectra, and displays normalized reference and experimental DISPA curves in both video and hard copy analog recorder form. In order to symmetrize the final display and reduce compu tation time, the procedure first narrows the frequency range to 20 dispersion peak-to-peak widths on either side of the absorption maximum. The absorption and dispersion baselines are then (separately) flattened. The true absorption peak height and position are accurately estimated usinga polynomial approximation near resonance. The algorithm then normalized the baseline-flattened absorption and dispersion data sets, and plots the corresponding DISPA curve superimposed on a reference circle whose diameter is the calculated absorption peak height. Spacing of the displayed DISPA data points automatically increases with the frequency separation from the center of resonance, for faster plotting and reduced redundancy in display. As a Pascal program, the procedure executes directly on a Bruker Aspect 2000 computer, and can readily be adapted to other computers with Pascal compilers.

Sparteine, a ligand for magnesium in organometallics: nuclear magnetic resonance studies of exchange

The15N resonances in reduced and oxidizedChromatium vinosum high-potential iron protein have been assigned by use of1H-1H COSY spectra and1H-15N HMQC, HMQC-COSY, and HMQC-NOESY spectra. Unambiguous assignment of 70 of 85 backbone15N resonances in the reduced protein and 62 of 85 resonances in the oxidized protein are made, as are 12 of 21 side-chain15N resonances.

CHARACTERIZATION OF A WATER-SOLUBLE, HELICAL BETA -PEPTIDE

The existence and structure, (I), of strong sparteine R2Mg complexes, which undergo inversion, carbon–magnesium bond exchange, and magnesium ligand exchange unusually slowly, have been established by n.m.r. studies.