Epoxide configuration in 3β-acetoxy-7α-hydroxy-14,15-epoxy-apotirucallane prepared from tirucalla-7,24-dien-3-one : X-ray analysis

Epoxidation of 3β - Acetoxy - 7α - hydroxy - Δ¹⁴ - apotirucallane, prepared from Δ7-tirucallone, afforded the corresponding 14α,15α epoxide. The α-configuration of the epoxide function has been established by single-crystal X-ray analysis, representing the first such study of a tirucallol derivative with an intact side-chain. Epoxidation of Apotirucalla - 3,7 - dione gave the corresponding 14α,15α - epoxide as well. Eight new tirucallol derivatives were described.     

Fourier and barycentric formulae for equidistant Hermite trigonometric interpolation

We consider the Hermite trigonometric interpolation problem of order 1 for equidistant nodes, i.e., the problem of finding a trigonometric polynomial t that interpolates the values of a function and of its derivative at equidistant points. We give a formula for the Fourier coefficients of t in terms of those of the two classical trigonometric polynomials interpolating the values and those of the derivative separately. This formula yields the coefficients with a single FFT. It also gives an aliasing formula for the error in the coefficients which, on its turn, yields error bounds and convergence results for differentiable as well as analytic functions. We then consider the Lagrangian formula and eliminate the unstable factor by switching to the barycentric formula. We also give simplified formulae for even and odd functions, as well as consequent formulae for Hermite interpolation between Chebyshev points.     

An efficient spectra processing method for metabolite identification from 1H-NMR metabolomics data

The spectra processing step is crucial in metabolomics approaches, especially for proton NMR metabolomics profiling. During this step, noise reduction, baseline correction, peak alignment and reduction of the 1D ¹H-NMR spectral data are required in order to allow biological information to be highlighted through further statistical analyses. Above all, data reduction (binning or bucketing) strongly impacts subsequent statistical data analysis and potential biomarker discovery. Here, we propose an efficient spectra processing method which also provides helpful support for compound identification using a new data reduction algorithm that produces relevant variables, called buckets. These buckets are the result of the extraction of all relevant peaks contained in the complex mixture spectra, rid of any non-significant signal. Taking advantage of the concentration variability of each compound in a series of samples and based on significant correlations that link these buckets together into clusters, the method further proposes automatic assignment of metabolites by matching these clusters with the spectra of reference compounds from the Human Metabolome Database or a home-made database. This new method is applied to a set of simulated ¹H-NMR spectra to determine the effect of some processing parameters and, as a proof of concept, to a tomato ¹H-NMR dataset to test its ability to recover the fruit extract compositions. The implementation code for both clustering and matching steps is available upon request to the corresponding author.

Near UV Spectra of the Aniliniums: φCH+ 2CH2X, φNH+ (CH2Xa)CH2Xb and φNH+ (C2H4)2X. Long Range Interactions Involving φ and X

We have shown in preceding papers^(1–3), in a study of some specific anilinium ions such as φNH⁺ _3-n (CH₃)_n, φ₂NH⁺ ₂ and φ₃NH⁺, that varying the ammonium groups, or the medium, can lead to great changes in the intensity of the secondary transition of the chromophore^(1–4) because of a δ, π coupling involving the substituent ^(1–10) and φ. In the present work we should like to extend our experiments to more complex ions - since apart our own works the UV spectroscopy of the aniliniums is almost unknown - to study the sensitivity of the chromophore to long range interactions with X through space or through the bonds of the substituents^(11–16).     

The Dualistic Nature of -NH3 +, A weak π-Donating,Strong σ-Withdrawing Substituent. Effects on the Intensity of the UV Spectra of the Toluidinium Ions and Related Molecules

Abstract

Hyperconjugation is not restricted to alkyl groups^(1–4) and ammoniums interact with π systems through σ-π hyperconjugative coupling^(5–9). Their influence on the UV spectrum of the secondary transition of the benzene chromophore in anilinium ions has only been studied during the last years. Previously it was assumed without enough experimental support, that ammonium groups have no spectroscopic effects on a π chromophore (for example:^(10,11)). In fact, although it is a strong σ-electronwithdrawing substituent, an ammonium group is a π-donating one ^5–8). Its π-donating ability - contrary to what is observed in the corresponding alkyl groups where N is replaced by C - increases whenever the number of N⁺?C bonds increases, and ?N(CH³)³+ could be as much π-donating as the ?C(CH₃)₃ group for pseudo-free molecules⁽⁵⁾.