Spectroscopic detection of chiral compounds is often hampered by a low sensitivity. For Raman optical activity (ROA), the signal can be dramatically increased in surface-enhanced experiments. So far, however, reproducible surface-enhanced ROA (SEROA) spectra were obtained for a reporter molecule only via induced chirality, and the intensities were just proportional to the Raman scattering. In the present study, we show that the signal can be substantially increased if colloidal silver nanoparticles are prepared already in the presence of a chiral analyte. In this case, both the analyte's and reporter's bands are visible. In addition, some experiments provided bisignate SEROA patterns, thus significantly enhancing information about the molecular structure provided by this spectroscopic method. Increased electronic circular dichroism (ECD) of the capped aggregated colloids suggests that ECD and polarized Raman scattering (ECD-Raman) contribute to the monosignate SEROA intensities, while well-dispersed nonaggregating colloids are important for observation of true (bisignate) molecular vibrational SEROA.

• Klíčová slova
• chiral analyte capped colloid, chirality, electronic circular dichroism, silver nanoparticles, surface-enhanced Raman optical activity,
• Publikační typ
• časopisecké články MeSH

Raman optical activity (ROA) is commonly measured with green light (532 nm) excitation. At this wavelength, however, Raman scattering of europium complexes is masked by circularly polarized luminescence (CPL). This can be avoided using near-infrared (near-IR, 785 nm) laser excitation, as demonstrated here by Raman and ROA spectra of three chiral europium complexes derived from camphor. Since luminescence is strongly suppressed, many vibrational bands can be detected. They carry a wealth of structural information about the ligand and the metal core, and can be interpreted based on density functional theory (DFT) simulations of the spectra. For example, jointly with ROA experimental data, the simulations make it possible to determine absolute configuration of chiral lanthanide compounds in solution.

• Klíčová slova
• Raman optical activity, chiral lanthanide complexes, circularly polarized luminescence, density functional theory, spectra simulations,
• Publikační typ
• časopisecké články MeSH