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International audience; RsEGFP2 is a reversibly photoswitchable fluorescent protein used in super-resolved optical microscopies, which can be toggled between a fluorescent On state and a nonfluorescent Off state. Previous time-resolved ultraviolet-visible spectroscopic studies have shown that the Off-to-On photoactivation extends over the femto- to millisecond time scale and involves two picosecond lifetime excited states and four ground state intermediates, reflecting a trans-to-cis excited state isomerization, a millisecond deprotonation, and protein structural reorganizations. Femto- to millisecond time-resolved multiple-probe infrared spectroscopy (TRMPS-IR) can reveal structural aspects of intermediate species. Here we apply TRMPS-IR to rsEGFP2 and implement a Savitzky-Golay derivative analysis to correct for baseline drift. The results reveal that a subpicosecond twisted excited state precursor controls the trans-to-cis isomerization and the chromophore reaches its final position in the protein pocket within 100 ps. A new step with a time constant of 42 ns is reported and assigned to structural relaxation of the protein that occurs prior to the deprotonation of the chromophore on the millisecond time scale.

This article highlights the importance of properly taking into account spatial structures and features to better resolve near-infrared (NIR) hyperspectral images by Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS), especially when highly mixed components (in terms of spatial and spectral overlap) underlying the systems under study are dealt with. As in the NIR domain these components can explain both chemical properties and physical phenomena, their improved unravelling can therefore represent an alternative or a complement to more standard approaches for, e.g., spectral data preprocessing. These points will be illustrated through the comprehensive analysis of a complex real-world forensic case-study where texture characterization is crucial for the sake of a more appropriate resolution. ispartof: ANALYTICA CHIMICA ACTA vol:1095 pages:30-37 ispartof: location:Netherlands status: published

This article explores smoothing with edge-preserving properties as a spatial constraint for the resolution of hyperspectral images with multivariate curve resolution–alternating least squares (MCR-ALS). For each constrained component image (distribution map), irrelevant spatial details and noise are smoothed applying an L1- or L0-norm penalized least squares regression, highlighting in this way big changes in intensity of adjacent pixels. The feasibility of the constraint is demonstrated on three different case studies, in which the objects under investigation are spatially clearly defined, but have significant spectral overlap. This spectral overlap is detrimental for obtaining a good resolution and additional spatial information should be provided. The final results show that the spatial constraint enables better image (map) abstraction, artifact removal, and better interpretation of the results obtained, compared to a classical MCR-ALS analysis of hyperspectral images.

International audience; In this paper, the combination of Two-Dimensional COrrelation Spectroscopy (2D-COS) and Multivariate Curve Resolution – Alternating Least Squares (MCR-ALS) is proposed to disentangle absorption and scattering contributions from extinction spectra collected during the synthesis of organic nanoparticles by laser ablation. This procedure relies on the fact that these contributions exhibit distinct dynamics in the synchronous and asynchronous modes of 2D-COS as the ablation proceeds. Thus, initial estimates for absorption and scattering spectral features can be discriminated and subsequently used when applying MCR-ALS analysis. The feasibility and the potential of this approach are demonstrated on a set of extinction spectra collected at different time intervals during the synthesis of dendronized perylenediimide (DPDI) nanoparticles. The time-dependent concentration profiles and spectra obtained provide valuable insights into the relative dynamics of its absorption and scattering. These results allow discussing the formation mechanism of DPDI nanoparticles.