Combination of Resonance and Non-Resonance Chiral Raman Scattering in a Cobalt(III) Complex

Raman scattering of water in vicinity of polar complexes: Computational insight into baseline subtraction

Water is a greatly convenient solvent in Raman spectroscopy. However, non-additive effects sometimes make its signal difficult to subtract. To understand these effects, spectra for clusters of model ions, including transition metal complexes and water molecules, were simulated and analyzed. A combined molecular mechanics/quantum mechanics approach was taken to reveal how relative Raman scattering intensities depend on the distance from the solute and the excitation wavelength. The computations indicate a big effect of solute charge; for example, the sodium cation affects Raman scattering by water to a lesser extent than the chlorine anion. The modeling was able to qualitatively reproduce the experimental observation that a solution of a simple salt may work as a baseline better than pure water in many Raman experiments. For absorbing species, an additional scattering boost occurs due to the resonance effect. Simulations thus provide useful insight into solute-solvent interactions and their effects on measured spectra.

Why Does One Measure Resonance Raman Optical Activity? A Unique Case of Measurements under Strong Resonance versus Far-from-Resonance Conditions

Raman optical activity (ROA) spectroscopy exhibits significant potential in the study of (bio)molecules as it encodes information on their molecular structure, chirality, and conformations. Furthermore, the method reveals details on excited electronic states when applied under resonance conditions. Here, we present a combined study of the far from resonance (FFR)-ROA and resonance ROA (RROA) of a single relatively small molecular system. Notably, this study is the first to employ the density functional theory (DFT) analysis of both FFR-ROA and RROA spectra. This is illustrated for cobalamin derivatives using near-infrared and visible light excitation. Although the commonly observed monosignate RROA spectra lose additional information visible in bisignate nonresonance ROA spectra, the RROA technique acts as a complement to nonresonance ROA spectroscopy. In particular, the combination of these methods integrated with DFT calculations can reveal a complete spectral picture of the structural and conformational differences between tested compounds.

Biomimetic SERS substrate with silicon-mediated internal standard: Improved sensing of environmental pollutants and nutrients

Biomimetic materials with fascinating natural micro-nano surface structures offer a good choice for the simple fabrication of surface-enhanced Raman scattering (SERS) substrate. This study presented a novel sodium carboxymethylcellulose (NaCMC)-Ag biomimetic substrate which was fabricated through the reverse replication of micro-nano structures from cantaloupe peel. Particularly, silicon nanoparticles (Si NPs) were doped into this flexible biomimetic substrate in its fabrication process. Abundant electromagnetic "hotspots" could be effectively excited in this Ag densely covered matrix which maintained numerous protrusions as well as vertical and horizontal grooves. Specifically, the doped Si NPs exhibited a robust intrinsic Raman peak, which could be employed as an internal standard to calibrate the target signal. In this regard, the biomimetic substrate with the optimal electromagnetic enhancement and the quantitative calibration capabilities exhibited a high enhancement factor and a remedied linear relationship in the detection. After a perfect uniformity of signal was proved by the corrected SERS mapping, the biomimetic SERS substrate was finally utilized in the practical analysis of methylene blue (MB) and β-carotene with ultra-low limit of detection, highlighting its importance in practical detection scenarios.