Univariate Statistical Analysis as a Guide to 1H-NMR Spectra Signal Assignment by Visual Inspection

In Proton Nuclear Magnetic Resonance (1H-NMR) spectroscopy, the signals assignment procedure is normally conducted by visual inspection of the spectra, by taking advantage of the innate predisposition of human eye for pattern recognition. In the case of untargeted metabolomics investigations on food and body fluids, the complexity of the spectra may lead the user to overlook signals, independently from their biological relevance. Here, we describe a four steps procedure that is designed to guide signals assignment task by visual inspection. The procedure can be employed whenever an experimental plan allows for the application of a univariate statistical analysis on a point-by-point basis, which is commonly the case. By comparing, as a proof of concept, 1H-NMR spectra of vaginal fluids of healthy and bacterial vaginosis (BV) affected women, we show that the procedure is also readily usable by non-experts in three particularly challenging cases: overlapping multiplets, poorly aligned signals, and signals with very poor signal-to-noise ratio. The paper is accompanied by the necessary codes and examples written in R computational language to allow the interested user gaining a hands-on impression of the procedure’s strengths and weaknesses.

ESR Study of Electron States in Ge/Si Heterostructures with Nanodisc Shaped Quantum Dots

Electron states in Ge/Si heterostructures with nanodisc shaped quantum dots (QDs) were studied using the electron spin resonance (ESR) method. Three ESR signals were observed under light illumination of the samples. The analysis of the angular dependences of the ESR spectra allows one performing signal assignment. Two ESR signals observed in the dark, as well as under illumination, are related to the electrons localized due to the strain at the top edges and base edges of the nanodiscs, while the third ESR signal observed only under illumination is related to the electrons localized in the Si layer above (or under) the central parts of the nanodiscs due to the Coulomb interaction with photoholes. A comparison with ESR results obtained for structures with lens-shaped QDs was performed. It was found that the nanodisc shape is crucial for the simultaneous localization of three electrons with different

Assigning NMR spectra of irregular RNAs by heuristic algorithms

Computer-aided analysis and preprocessing of spectral data is a prerequisite for any study of molecular structures by Nuclear Magnetic Resonance (NMR) spectroscopy. The data processing stage usually involves a considerable dedication of time and expert knowledge to cope with peak picking, resonance signal assignment and calculation of structure parameters. A significant part of the latter step is performed in an automated way. However, in peak picking and resonance assignment a multistage manual assistance is still essential. The work presented here is focused on the theoretical modeling and analyzing the assignment problem by applying heuristic approaches to the NMR spectra recorded for RNA structures containing irregular regions.