Heuristic charge assignment for deconvolution of electrospray ionization mass spectra

We propose a new algorithm for deconvolution of electrospray ionization mass spectra based on direct assignment of charge to the measured signal at each mass-to-charge ratio (m/z). We investigate two heuristics for charge assignment: the entropy-based heuristic is adapted from a deconvolution algorithm by Reinhold and Reinhold;10 the multiplicative-correlation heuristic is adapted from the multiplicative-correlation deconvolution algorithm of Hagen and Monnig.6 The entropy-based heuristic is insensitive to overestimates of z(max), the maximum ion charge. We test the deconvolution algorithm on two single-component samples: the measured spectrum of human beta-endorphin has two prominent and one very weak line whereas myoglobin has a well-developed quasi-gaussian envelope of 17 peaks. In both cases, the deconvolution algorithm gives a clean deconvoluted spectrum with one dominant peak and very few artefacts. The relative heights of the peaks due to the parent molecules in the deconvoluted spectrum of a mixture of two peptides, which are expected to ionize with equal efficiency, give an accurate measure of their relative concentration in the sample.     

Thermoregulatoren

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Determination of absolute configurations from vibrational raman optical activity: (trans)-2,3-dimethylthiirane

Experimental and theoretical vibrational Raman optical activity (VROA) spectra of (2R,3R)-2,3-dimethylthiirane in the 200-1500 cm(-1) region are presented. The level of agreement obtained for the observed and predicted VROA signs suggests that the absolute configurations of chiral molecules can be determined confidently using VROA.     

Rapid screening procedures for the hydrolysis products of chemical warfare agents using positive and negative ion liquid chromatography-mass spectrometry with atmospheric pressure chemical ionisation

Qualitative screening procedures have been developed for the rapid detection and identification of the hydrolysis products of chemical warfare agents in aqueous samples and extracts, using liquid chromatography-mass spectrometry with positive and negative atmospheric pressure chemical ionisation (APCI). Previously reported screening procedures, which used positive APCI or electrospray ionisation (ESI), were modified by using LC conditions that allowed acquisition of positive and negative ion mass spectra. APCI was generally found to be more robust than ESI, probably due to variable adduct ion formation with ESI, depending on the condition of the sample and the system. Negative APCI provided selective detection of acidic analytes and allowed facile differentiation of alkyl alkylphosphonic acids from isomeric dialkyl alkylphosphonates. The combination of positive and negative APCI, using a C18 column and water-methanol mobile phase modified with ammonium formate, provides a rapid screening procedure for chemical warfare agent degradation products, with limits of detectability in the range 10-100 ng/ml. In the case of proficiency test samples, where analyte concentrations are in the range 1-10 ppm, introduction of the sample by infusion may provide an even faster preliminary screening procedure.     

An electron-optical study of nickel monosulfide

The high temperature form of nickel monosulfide, Ni_(1?x)S has the nickel arsenide structure. It is nonstoichiometric in the range NiSNi_0.91S. Powder X-ray diffraction of synthetic samples suggests a simple solid solution, but high resolution electron microscopy reveals three different structural regions. One of these, previously reported elsewhere, has rhombohedral symmetry with a 3 × a repeat. The second region shows a 2 × a repeat, while the third appears to contain disordered vacancies. The effect of multiple scattering on the electron diffraction patterns and images is discussed.     

ACTION SPECTRUM AND THRESHOLD SENSITIVITY OF ENTRAINMENT OF ORCADIAN RUNNING ACTIVITY IN THE COCKROACH PERIPLANETA AMERICANA

Abstract— The interaction between the compound eye and the circadian timing system for running activity in the cockroach, Periplaneta americana , has been investigated by measuring the action spectrum for entrainment of such behavior by imposed photic stimuli. Test wavelengths were selected which spanned the spectral range of the dichromatic retina of this insect and intensities of such lights for which half of a population of animals failed to be entrained (threshold) were determined. Stimuli were presented either with a 12:12 light–dark regime or for 12h/day on a continuous background of orange light. The latter procedure altered the balance of sensitivity in the two groups of color receptors in the eye. A comparison of the resulting action spectra and the spectral sensitivities of receptors and visual interneurons measured under similar conditions suggest that the entrainment mechanism is dominated by the receptor group most sensitive to long wavelength light. Furthermore, the eye-clock mechanism shows an extraordinarily high sensitivity to such stimuli. We estimate that a mean flux of about 5 photons/eye/s is sufficient to entrain the behavior. The implications of these results are discussed.     

Synthesis and utilisation of 2,7′-diindolylmethanes and a 2-(2-indolyl)pyrrolylmethane as macrocyclic precursors

Treatment of 3-(4-chlorophenyl)-7-hydroxymethyl-4,6-dimethoxyindole with 3-(4-chlorophenyl)-4,6-dimethoxyindole results in the generation of two geometrically isomeric diindolylmethanes in addition to a novel triindolyl oligomer, which has been structurally characterised. The 2,7′-diindolylmethanes were found to be unstable under Vilsmeier formylation conditions, thus hampering macrocyle precursor construction. In an alternate approach, the 3-(4-chlorophenyl)-4,6-dimethoxyindole-7-carbaldehyde was converted into the indolyl-pyrrolyl macrocycle precursor 5-(3-(4-chlorophenyl)-4,6-dimethoxyindole-2-ylmethyl)-4-ethyl-3-methylpyrrole-2,7-dicarbaldehyde, which was used to generate an unsymmetrical pentaaza macrocycle.     

Error-free storage compression of binary-coded infrared spectra

Microcomputer systems are increasingly being used to acquire and store digital spectral data, and computerised data bases and spectral libraries are valuable in the identification of sample spectra. Access to the original recorded data is essential, so problems of storing large volumes of spectral data arise. To alleviate such problems partly, erorr-free data-compression schemes based on Huffman shift coding are tested on infrared spectra. The results indicate that substantial savings, up to 70%, of the digital memory requirements can be achieved by using error-free coding techniques. Part of this saving is attributed to data compression of oversampled regions of digitised spectra. Compressed spectral data can not only be stored more efficiently but also provide increased data-transfer rates between computer systems.