Transfer RNA modifications play pivotal roles in protein synthesis. N6-threonylcarbamoyladenosine (t6A) and its derivatives are modifications found at position 37, 3΄-adjacent to the anticodon, in tRNAs responsible for ANN codons. These modifications are universally conserved in all domains of life. t6A and its derivatives have pleiotropic functions in protein synthesis including aminoacylation, decoding and translocation. We previously discovered a cyclic form of t6A (ct6A) as a chemically labile derivative of t6A in tRNAs from bacteria, fungi, plants and protists. Here, we report 2-methylthio cyclic t6A (ms2ct6A), a novel derivative of ct6A found in tRNAs from Bacillus subtilis, plants and Trypanosoma brucei. In B. subtilis and T. brucei, ms2ct6A disappeared and remained to be ms2t6A and ct6A by depletion of tcdA and mtaB homologs, respectively, demonstrating that TcdA and MtaB are responsible for biogenesis of ms2ct6A.

The impact of the vibrational coupling of the OH stretch mode on the spectra differs significantly between IR and Raman spectra of water. Unified understanding of the vibrational couplings is not yet achieved. By using a different class of vibrational spectroscopy, hyper-Raman (HR) spectroscopy, together with machine-learning-assisted HR spectra calculation, we examine the impact of the vibrational couplings of water through the comparison of isotopically diluted H 2 O and pure H 2 O. We found that the isotopic dilution reduces the HR bandwidths, but the impact of the vibrational coupling is smaller than in the IR and parallel-polarized Raman. Machine learning HR spectra indicate that the intermolecular coupling plays a major role in broadening the bandwidth, while the intramolecular coupling is negligibly small, which is consistent with the IR and Raman spectra. Our result clearly demonstrates a limited impact of the intramolecular vibration, independent of the selection rules of vibrational spectroscopies.

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We report hyper‐Raman (HR) spectra of concentrated hydrochloric acid solutions for the first time. HR signals from the OH stretching region to the low‐frequency region reflect the presence of chloride anions solvated in water. By contrast, it turns out that HR spectroscopy is insensitive to the presence of excess protons in water. HR spectra of HCl solutions do not show any signature of a proton continuum and shoulders on the high/low‐frequency sides of the bending mode of H2O in stark contrast to IR spectroscopy. Moreover, we found that a sharp HR signal around 500 cm−1 appear in 532 nm excited HR spectra. A laser power dependence indicates that this signal comes from a photochemical reaction. The absence of this signal under 1064 nm HR excitation and 532 nm Raman excitation suggests that the resonance (hyper‐)Raman effect enhances the signal from the photoproduct.