Properties of Gaseous Deprotonated L-Cysteine S-Sulfate Anion [cysS-SO3]−: Intramolecular H-Bond Network, Electron Affinity, Chemically Active Site, and Vibrational Fingerprints
, Gao-Lei Hou 2, Zheng Yang 2, Marat Valiev 3,*, Xue-Bin Wang 2,*, Xianfeng Zheng 1 and Zhifeng Cui 1Round 1
Reviewer 1 Report
Recommendation: This paper is publishable only after addressing the requested issues. Further review is needed.
In this manuscript, Wang et al. report the photoelectron spectroscopy of trapped [cysS-SO3]‒ ion at T =20K using a magnetic bottle spectrometer and excimer lasers. Numerous computations are performed to explain the experimental results. Here are some observations that may help to improve the manuscript further.
1. Page -1 : In the abstract “The most reactive site of the molecule susceptible for electrophilic attacks is the linkage S atom. Theoretically predicted infrared spectra indicate O−H and N−H stretching modes are the fingerprint region (2800 to 3600 cm-1) to distinguish different isomers.” These two sentences require further emphasis otherwise seems disconnected. It is not clear why electrophilic attacks are suddenly important and why we need know about multiple conformations (likely the torsional modes as described later in the manuscript).
2. Page -3, in the results are discussion it is written, “Three spectral bands X, A, and B are observed at 157 nm in the EBE range of 5.0 to 7.6 eV, while only band X and the rising edge of band A are seen in the 193 nm spectrum.” Please clarify X, A, and B are electronic states are belong to the neutral or anion.
3. page – 3, “The X band peak position of 5.30(10) eV was assigned to the experimental VDE (see Table 1),” It is likely the excimer lasers has pulse duration of the order of nanoseconds. It is likely after the ionization of the anion, it will attain the equilibrium geometry in the neutral state, therefore, the transition is expected to be adiabatic. Usually the vertical transition happens while using ultrafast femtosecond laser pulses. Please clarify this assignment of VDE.
4. Page -3, several numbers are mentioned like 4.95, 5.30, 6.60 eV with “(10)” which is not understood.
5. Page – 3, please format the Table properly. Some of the numbers are not in proper row e.g. S3, S8, S9. Please explain how 20 different conformation are searched before optimization and how it was ensured that they are the unique 20 minimal energy conformers after optimization. Did the author estimate the thermal population of these conformers at 20 K?
6. Page -5, there are six simulated DOS stick (thin red) in Figure 3. Please explain them.
7. Page -6, “It is worth noting that the global minimum of the anion S1 is stabilized through the formation of three intramolecular hydrogen bonds (HBs); one of them comes from amino N playing the acceptor role of HB (O−H---N) and the rest from two amino H acting as HB donors to −SO3.” This claim is without any supporting evidence. Therefore, the authors are requested to move the NBO and QTAIM analysis, and Table S2 as a supporting evidence here, i.e. before discussing the simulated IR spectra. Tabulate the non covalent delocalization energy from NBO analysis also.
8. Page – 8, please explain/introduce the various terms used in QTAIM analysis.
9. Page – 9, “For the most stable conformer S1, a novel intramolecular HB network is revealed,” please explain why do authors think that this is “a novel intramolecular HB network”? This is only a conventional NH---O hydrogen bond network.
Author Response
see attached letter
Author Response File: 
Author Response.docx
Reviewer 2 Report
This paper is generally acceptable for publication as submitted but the Introduction is very poorly written. Basically the number of sentences should be doubled and only one main point should be conveyed by each sentence.
The Introduction needs a complete rewrite, after which publication should be possible.
Author Response
see attached letter
Author Response File: Author Response.docx
