Nuclear magnetic resonance of phosphorus compounds: 9—The NMR spectra of phosphirane

The 100 MHz proton and 40.4 MHz ³¹P NMR spectra of phosphirane (1) have been recorded at ?20 °C and analysed iteratively to yield coupling constants and chemical shifts. The 22.6 MHz ¹³C spectrum of 1 was recorded at 0 °C and analyzed. The ³¹P chemical shift of 1 was measured as 40 467 515.97 ± 0.08 Hz relative to TMS as 100 000 000.00 Hz. The geminal P-C-H couplings in 1 are opposite in sign and of different magnitudes (+16.14 and ?2.64 Hz); the P? H coupling (+158.34 Hz) is smaller than that in any other organic phosphine. These observations are discussed and correlated with the geometry of 1. The electronic structure of the strained ring of 1 is discussed in terms of a localized valence bond approach.     

On the potential carcinogenic and mutagenic character of benzobiphenylenes

PMO estimations suggest certain partially saturated benzobiphenylene carbonium ions might exhibit carcinogenic and/or mutagenic activity.     

The 14N NMR linewidth versus pH profiles for several amino acids

A spectrometer for recording ¹⁴N NMR spectra is described. The ¹⁴N NMR linewidth versus pH dependences of several amino acids and related molecules are presented. It appears that the linewidth pH profile of each amino acid is unique. Linewidth minima occur between pH 6 and 8. A discussion on how ¹⁴N NMR linewidths of amino acids might give information on weak association is given.     

A new approach to variable selection in least squares problems

The title Lasso has been suggested by Tibshirani (1996) as acolourful name for a technique of variable selection which requiresthe minimization of a sum of squares subject to an l₁ bound on the solution. This forces zero components in the minimizingsolution for small values of . Thus this bound can functionas a selection parameter. This paper makes two contributionsto computational problems associated with implementing the Lasso:(1) a compact descent method for solving the constrained problemfor a particular value of is formulated, and (2) a homotopymethod, in which the constraint bound becomes the homotopyparameter, is developed to completely describe the possibleselection regimes. Both algorithms have a finite terminationproperty. It is suggested that modified Gram-Schmidt orthogonalizationapplied to an augmented design matrix provides an effectivebasis for implementing the algorithms.     

Siderophore-Mediated Iron Uptake Promotes Yeast–Bacterial Symbiosis

In the present study, siderophore produced by the marine yeast Aureobasidium pullulans was characterized as hydroxamate by chemical and bioassays. The hydroxamate assignment was supported by the appearance of peaks at 1,647.21?C1,625.99?cm^?1 and at 1,435.04?cm^?1 in the infrared spectrum. The purified siderophore exhibited specific growth-promoting activity under iron-limited conditions for siderophore auxotrophic probiotic bacteria. Cross-utilization of siderophore indicates a symbiotic relationship between the yeast A. pullulans and the selected probiotic bacterial strains. Statistical optimization of medium components for improved siderophore production in A. pullulans was depicted by response surface methodology. The shift in UV?CVis spectroscopy indicates the photoreactive property and subsequent oxidative cleavage of purified siderophore on exposure to sunlight.     

Flux line lattice symmetries in the borocarbide superconductor LuNi2B2C

We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor LuNi₂B₂C with the applied field along the c- and a-axes. For H‖c the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above 10 K the transition onset field. H ₂(T), rises sharply, bending away from H _c2(T) in contradiction to theoretical predictions of the two merging. For H‖a a first order FLL reorientation transition is observed at H _tr=3–3.5 kOe. Below H _tr the FLL nearest neighbor direction is parallel to the b-axis, and above H _tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model.     

A detailed evaluation of the dependence of 3J(H?H) on bond angle in alkenes and cycloalkenes

Newly determined and accurate data for the magnitudes of cis vinyl proton-proton spin-spin coupling constants in cis-dialkylethylenes and cycloalkenes have been obtained. With these new data and also values taken from the recent literature, it has proved possible to make a critical determination of the correlation between ³J(H? H) and C?C? H bond angles in ethylenic systems. It is suggested that it is possible to obtain accurate estimates of bond angles using NMR coupling constants, even though much more data will be required to fully substantiate this proposal. Whereas cis-³J(H? H) decreases rapidly with increasing C?C? H bond angles, evidence is presented that the opposite is the case for trans-³J(H? H). A brief theoretical discussion of these trends in coupling constants is given.     

Electron spin resonance of manganous ions in frozen methanol solution

An analysis of the electron spin resonance of Mn²⁺ in frozen methanol is presented. The broadened, asymmetric lineshape is shown to be due to inhomogeneous broadening caused by combined second - and third-order effects of randomly distributed zero-field splittings in the range of 80-150 G.     

On the analyses of mixture vapor pressure data: the hydrogen peroxide/water system and its excess thermodynamic functions

Reported here are some aspects of the analysis of mixture vapor pressure data using the model-free Redlich-Kister approach that have heretofore not been recognized. These are that the pure vapor pressure of one or more components and the average temperature of the complex apparatuses used in such studies can be obtained from the mixture vapor pressures. The findings reported here raise questions regarding current and past approaches for analyses of mixture vapor pressure data. As a test case for this analysis approach the H2O2-H2O mixture vapor pressure measurements reported by Scatchard, Kavanagh, and Tickner (G. Scatchard, G. M. Kavanagh, L. B. Ticknor, J. Am. Chem. Soc. 1952, 74, 3715-3720; G. M. Kavanagh, PhD. Thesis, Massachusetts Institute of Technology (USA), 1949) have been used; there is significant recent interest in this system. It was found that the original data is fit far better with a four-parameter Redlich-Kister excess energy expansion with inclusion of the pure hydrogen peroxide vapor pressure and the temperature as parameters. Comparisons of the present results with the previous analyses of this suite of data exhibit significant deviations. A precedent for consideration of iteration of temperature exists from the little-known work of Uchida, Ogawa, and Yamaguchi (S. Uchida, S. Ogawa, M. Yamaguchi, Japan Sci. Eng. Sci. 1950, 1, 41-49) who observed significant variations of temperature from place to place within a carefully insulated apparatus of the type traditionally used in mixture vapor pressure measurements. For hydrogen peroxide, new critical constants and vapor pressure-temperature equations needed in the analysis approach described above have been derived. Also temperature functions for the four Redlich-Kister parameters were derived, that allowed calculations of the excess Gibbs energy, excess entropy, and excess enthalpy whose values at various temperatures indicate the complexity of H2O2-H2O mixtures not evident in the original analyses of this suite of experimental results.