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Data Files Accompanying: "Molecular-level Origin of the Carboxylate Head Group Response to Divalent Metal Ion Complexation at the Air-water Interface"

Authors: Joanna K. Denton, Patrick J. Kelleher, Marcel D. Baer, Shawn M. Kathmann, Christopher J. Mundy, Bethany A. Wellen Rudd, Heather C. Allen, Tae Hoon Choi, Kenneth D. Jordan, and Mark A. Johnson

Journal: Proceedings of the National Acadamy of Sciences of the United States of America (PNAS)

Contact:
Mark A. Johnson, mark.johnson@yale.edu, Sterling Chemistry Laboratory, Yale University

Cite as: Denton, Joanna, K.; Kelleher, Patrick, J.; Baer, Marcel, D.; Kathmann, Shawn, M.; Mundy, Christopher, J.; Wellen Rudd, Bethany, A.; Allen, Heather, C.; Choi, Tae, Hoon; Jordan, Kenneth, D.; Johnson, Mark, A. (2019). Data from: Molecular-level Origin of the Carboxylate Head Group Response to Divalent Metal Ion Complexation at the Air-water Interface. In Center for Aerosol Impacts on Chemistry of the Environment (CAICE). UC San Diego Library Digital Collections. https://doi.org/10.6075/J0JQ0Z7C


Naming Scheme:

	Experimental data files are named following the general format: 
[method]_[metal (if any)]_[carboxylate abbreviation]_H2O_[hydration number]_[tag or specification of multiphoton dissociation(MPD)]_[trap temperature].csv
In cases where none of the species were hydrated, species were not tagged (as in IRRAS) or temperature was not crucial, these elements were omitted.
	
	Columns in data files often use a string to identify the species for which the data was taken before appending the variable name. These strings follow the general format:
[metal (if any)]_[carboxylate abbreviation]_H2O_[hydration number]_[isomer designation (if any)]_[tag or specification of multiphoton dissociation(MPD)]_[trap temperature]
In cases where none of the species were hydrated, species were not tagged (as in IRRAS) or temperature was not crucial, these elements were omitted.
Carboxylate abbreviations are as follows:
	dOPr=d5-propionate
	HCOO-=Formate
	CH3COO-=Acetate
	CH3(CH2)10COO-=Dodecanoate
	d31-PA=d31-Palmitic acid
	d35-SA=d35-Stearic acid


File Organization and Contents:

Experimental Data:
IRRAS_d31-PA_d35-SA_d31-PACaCl2.csv contains the IRRAS spectra of neat d31-PA on H2O, d35-SA on pD 10.5 D2O, and d31-PA on 0.3 M CaCl2 in D2O necessary to reproduce figures 1, 3(j), and 5(k).  
CIVP_dOPr_H2O_n_D2_20K.csv contains the CIVP spectra for CD3CD2COO¯·(H2O)n=0-7,14 D2 tagged necessary to reproduce figures 3 and 4(e) and 5(a).
CIVP_Ca_dOPr_H2O_n_He-H2_20K.csv contains the CIVP spectra for CaCD3CD2COO+·(H2O)n=0-5 He and H2 tagged  necessary to reproduce figure 5(b-g), and S2(a) 
IRMPD_Ca_dOPr_H2O_n_MPD_20-100K.csv contains the IRMPD spectra for CaCD3CD2COO+·(H2O)n n= 5, 6, 8, 10, 12, 13 at 20 K and hydration n=5 at 100 K necessary to reproduce figures 5(h-j), and S2(b-c).
CIVP_HCOO-_Ar_CH3COO-_H2_CH3(CH2)10COO-_H2.csv contains the CIVP spectra for HCOO¯ Ar tag, CH3COO¯ H2 tag, and CH3(CH2)10COO¯ H2 tag necessary to reproduce figure S1
CIVP_ALL_PeakPositions.csv contains all CIVP and IRMPD peak positions at 20 K necessary to reproduce figures 6, 7 and 8 and reproduced in tables S2 and S3.
LIT_ALL_PeakPositions.csv contains all peak positions obtained from literature used to position arrows and lines in figures 3, 5 and 7 and referenced in table S1. For information on how these values were obtained, see “Notes on The Extraction of Experimental Symmetric and Asymmetric Carboxylate Stretches for Inclusion in Figure 1” near the end of this document.

Calculations:	
ElectFieldProjection_BareAndCa_dOPr_H2O_n.csv contains the magnitude of the projections of the electric field along the C1-C2, C1-O1, and C1-O2 axis for dOPr¯·(H2O)n=0-5 and CadOPr+·(H2O)n=0-6 necessary to reproduce figures 7 and S4.
GaussianFreq_MP2_aug-cc-pVDZ_dOPr_H2O_0.csv contains the calculated IR modes featured in figures 3(a) and 5(a)
GaussianFreq_MP2_aug-cc-pVDZ_dOPr_H2O_1.csv contains the calculated IR modes featured in figure 3(b)
GaussianFreq_MP2_aug-cc-pVDZ_dOPr_H2O_2.csv contains the calculated IR modes featured in figure 3(c)
GaussianFreq_MP2_aug-cc-pVDZ_dOPr_H2O_3.csv contains the calculated IR modes featured in figure 3(d)
GaussianFreq_MP2_aug-cc-pVDZ_dOPr_H2O_4.csv contains the calculated IR modes featured in figure 3(e)
GaussianFreq_MP2_aug-cc-pVDZ_dOPr_H2O_5_3+1.csv contains the calculated IR modes for the "3:1" structure, featured in figures 3(f) and 4(d)
GaussianFreq_MP2_aug-cc-pVDZ_dOPr_H2O_5_2+2.csv contains the calculated IR modes for the "2:2" structure, featured in figure 4(c)
GaussianFreq_MP2_aug-cc-pVDZ_dOPr_H2O_6.csv contains the calculated IR modes featured in figure 3(g)
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_0.csv contains the calculated IR modes featured in figure 5(b)
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_1.csv contains the calculated IR modes featured in figure 5(c)
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_2.csv contains the calculated IR modes featured in figure 5(d)
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_3.csv contains the calculated IR modes featured in figure 5(e)
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_4.csv contains the calculated IR modes featured in figure 5(f)
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_5.csv contains the calculated IR modes featured in figure 5(g)
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_6_CP6-1.csv contains calculated IR modes featured in figures 5(h) and 8
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_6_CP6-3.csv contains calculated IR modes necessary to reproduce figure 8
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_6_CP6-4.csv contains calculated IR modes necessary to reproduce figure 8
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_8_CP8-1.csv contains calculated IR modes necessary to reproduce figure 8
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_8_CP8-4.csv contains calculated IR modes necessary to reproduce figure 8
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_8_CP8-6.csv contains calculated IR modes necessary to reproduce figure 8
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_10_CP10-1.csv contains the calculated IR modes featured in figures 5(i) and 8
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_10_CP10-2.csv contains calculated IR modes necessary to reproduce figure 8
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_10_CP10-4.csv contains calculated IR modes necessary to reproduce figure 8
GaussianFreq_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_12.csv contains the calculated IR modes featured in figures 5(j) and 8
GaussianOpt_MP2_aug-cc-pVDZ_dOPr_H2O_n.csv contains the cartesian coordinates of the calculated structures of hydration numbers 0-6 necessary to reproduce figure 2(a) and (c), the figure 3 inset, figure 4(a) and (b), figure S3, and corresponding to the calculated IR modes seen in figure 3.
GaussianOpt_MP2_aug-cc-pVDZ_Ca_dOPr_H2O_n.csv contains the cartesian coordinates of the calculated structures of hydration numbers 0-12 necessary to reproduce figure 2(b) and (d), the figure 5 and 8 insets, figures S5 and S6, and corresponding to the calculated IR modes seen in figures 5 and 8.
GaussianOpt_CAM-B3LYP_6-311++g(3pd,3df)_HCOO-_CH3COO-_CH3(CH2)10COO-.csv contains the cartesian coordinates necessary to reproduce insets in figure S1.


Experimental and Computational Methods:
IRRAS Experimental Method:
	For the IRRAS studies, deuterated palmitic acid (d31-PA, >98%, Cambridge Isotopes Laboratories) was dissolved in chloroform (HPLC grade, Fisher Scientific) at a concentration of approximately 2 mM and was spread, using a 50 microliter syringe (Hamilton), to a mean molecular area of 20.5 (Å^2)/molecule on a petri dish containing 0.3 M solutions of CaCl2•2H2O (>99%, ACS Certified, Fisher Scientific, CAS 10035-.4-8) in D2O (99%, Sigma Aldrich, 7789-20-0). Salts were used as received without further purification (1). Deuterated stearic acid (d35-SA, >98%, Cambridge Isotopes Laboratories) was also dissolved to 2 mM in chloroform and spread onto a pD 10.5 subphase (2, 3), adjusted with NaOD (>99%, Acros Organics, 14014-06-3), to observe the bare carboxylate modes without additional metal ions present. The longer chain stearic acid was used for this because it has been previously shown that fully deprotonated palmitic acid desorbs from the interface and cannot be observed within the limits of detection of the IRRAS system (4). 
	IRRAS spectra were collected with a custom built setup situated in an FTIR spectrometer (Spectrum 100, Perkin Elmer). The setup consists of two planar gold mirrors, the first of which directs the incoming unpolarized IR beam to the sample surface at a 45° angle of incidence relative to surface normal (5). The second mirror directs the reflected radiation to a liquid nitrogen cooled MCT detector. Due to possible HOD interferences in the spectra from the adsorption of atmospheric water vapor to the D2O surface (6), the spectrometer chamber was purged with a constant flow of nitrogen and sealed with plastic during the course of the measurement. 
Each spectrum was collected over the range of 4000-450 cm-1, at 4 cm-1 resolution, and is the result of coaveraging 300 scans. The spectra shown here are the average of at least 3 individual trials which have been baseline corrected by a third-order polynomial prior to averaging. IRRAS spectra are represented in terms of reflectance-absorbance (RA=-log(R/R0)), where the R is the reflectance of the monolayer-covered surface and that of the bare surface is R0. 

IR Spectroscopy of Gas-phase Cluster Ions Method:
	Solution preparation methods were optimized to the species of interest. To prepare small dehydrated and monohydrated d5-propionic acid (denoted d-OPr¯) clusters for CIVP, a solution of ~1-2 mM Na+ d-OPr¯ in methanol was prepared. Larger hydrated clusters d-OPr¯ clusters were obtained using a solution of ~2 mM Na+ d-OPr¯ in 9:1 acetonitrile to H2O. To prepare Ca2+ d-OPr¯ clusters for CIVP, solutions of ~0.5-1 mM calcium hydroxide and ~1-2 mM d-OPr¯ in H2O were used. IRMPD on larger clusters used solutions of 1.2 mM calcium hydroxide and 2 mM d-OPr¯ in H2O. 
	The combination of mass spectrometry and optical spectroscopy methods used here have been described in detail previously (7), and measure vibrational spectra of size-selected ions using a double-focusing, tandem time-of-flight photofragmentation mass spectrometer. Briefly, ions are extracted from ~1-2 mM solutions using electrospray ionization, water condenses around these ions in the humidity controlled electrospray capsule, and clusters are accumulated in a variable temperature (10 - 100 K) radiofrequency ion trap for ~100 ms. During this period, He buffer gas was pulsed into the trap to slow and collisionally cool the ions to ~20 K before injection into the time-of-flight region. The spectra of the small clusters yield structural information about strongly bound water molecules in the first hydration shell and were therefore obtained using the mass “tagging” cold ion vibrational spectroscopy (CIVP) technique. In this approach, vibrational spectra of the cold ions are acquired in a linear action mode through photoevaporation of a weakly bound adduct condensed on the cluster in the ion trap (in the present case, He, H2, or D2). For larger clusters, which were produced in decreasing abundance in the mass spectrometer, the spectra were obtained by monitoring the infrared multiple photon-induced dissociation (IRMPD) of a more weakly bound water molecule in the second hydration shell. The spectra band maxima, are very similar for the two methods (difference of < 7 cm-1), and the observed bands are found to be quite insensitive to temperature from 20 to 100 K. 
	Data was obtained by averaging 4 to 10 scans together for CIVP and between 30 and 90 scans for IRMPD. The obtained intensities were divided by the laser power, and normalized to unity. The IRMPD intensities were then smoothed using 3 point adjacent averaging. The frequency uncertainty for the CIVP and IRMPD data is ±3 cm-1 based on the linewidth of the laser used.

Computation of CD3CD2COO¯·(H2O)n=0-6 Structures and Frequencies: 
	For each of the CD3CD2COO¯·(H2O)n, n = 0 - 6 (denoted d-OPr¯·(H2O)n= 0 - 6), clusters several possible structures were built by hand and optimized using the B3LYP density functional method (8-10) with the D3 correction for dispersion method (11, 12) in conjunction with the aug-cc-pVDZ basis set (13, 14). For each of these isomers, vibrational frequencies and IR intensities were calculated in the double harmonic approximation at the same level of theory. For the CD3CD2COO¯·(H2O)n, n = 0 - 4 and 6, clusters, the lowest energy isomers identified give calculated vibrational spectra in qualitative agreement with the measured vibrational spectra. However, for no choice of isomers generated in the manner described above were the calculations successful at accounting for the observed non-monotonic trend in the CO stretch frequencies along the n = 4 - 6 sequence. This led us to conclude that the isomer responsible for the observed spectrum of the n = 5 cluster was not included in the initial set of isomers considered. To search for other low-energy isomers of the n= 5 cluster, we undertook NVT molecular dynamics (MD) simulations of CD3CD2COO¯·(H2O)5 at T = 300 K. The MD simulations were started from the lowest energy structure found by minimization of hand-built structures and were carried out using the B3LYP method in conjunction with the 6-31G(d) basis set (15). The integration time step was 1 fsec, and the total simulation time was 23 ps. Low-energy structures were extracted from the MD trajectory and optimized at the B3LYP+D3/aug-cc-pVDZ level of theory. 
	The structures of the low-energy isomers of the CD3CD2COO¯·(H2O)5 clusters obtained in the B3LYP+D3/aug-cc-pVDZ optimizations were reoptimized at the MP2/aug-cc-pVDZ level(16). Harmonic vibrational spectra were calculated using both the B3LYP+D3 and MP2 methods together with the aug-cc-pVDZ basis set. In addition, for the isomers identified for the n = 5 clusters, single-point calculations using the MP2/aug-cc-pVDZ geometries were also carried out at the MP2 method with the aug-cc-pVTZ basis set (13, 14) and the coupled cluster with single and double excitations with perturbative triples (17) with explicit F12 correlation (18) together with the VDZ-F12 basis set (19). The CCSD(T)-F12b/VDZ-F12 method is expected to give CCSD(T) energies close to those that would be obtained with the aug-cc-pVQZ basis set (13, 14). Counterpoise corrections (20) for basis set superposition error (BSSE) were applied to the B3LYP+D3 and MP2 energies. All MP2 and CCSD(T) calculations were carried out in the frozen-core approximation. For the most stable isomers identified for the CD3CD2COO¯·(H2O)n n = 1 - 6,  clusters harmonic and anharmonic vibrational spectra were also calculated. The anharmonic spectra were calculated using the second-order vibrational perturbation theory (VPT2) method (21). The B3LYP and MP2 geometry optimizations and harmonic vibrational frequency calculations described for CD3CD2COO¯·(H2O)n=0-6 and for CaCD3CD2COO¯·(H2O)n=0-12 were carried out using the Gaussian 16 program (22), and the MD simulations were carried out using GAMESS (23). The CCSD(T)-F12 calculations were carried out using the MOLPRO program(24). A scaling factor of 0.986 was used for MP2 spectral results. 

Computation of d-[Ca2+ OPr¯]+·(H2O)n=0-6,8,10,12 Structures and Frequencies
For the CaCD3CD2COO¯·(H2O)n, n=1-5 clusters,(denoted d-[Ca2+ OPr¯]+·(H2O)n=1-5) several possible structures were built by hand and optimized at the MP2/aug-cc-pVDZ and B3LYP+D3/aug-cc-pVDZ levels of theory. For the n = 6, 8, 10 and 12 clusters NVT molecular dynamics (MD) simulations at T = 300 K for over 15 ps using the B3LYP/6-31G(d) level of theory. The MD simulations were started from both monodentate and bidentate binding configurations. Low-energy structures extracted from the MD trajectories were optimized and calculated for the harmonic vibrational spectra using both the B3LYP+D3 and MP2 methods together with the aug-cc-pVDZ basis set. In applying the frozen core approximation in the MP2 calculations, the 3s and 3p orbitals of the Ca atoms were retained in the valence space. A scaling factor of 0.986 was used for MP2 spectral results. To ensure that the calculated frequencies could be compared directly to the experimental linear action spectra, the predicted IR intensities were divided by their associated vibrational frequencies (25).

Notes on The Extraction of Experimental Symmetric and Asymmetric Carboxylate Stretches for Inclusion in Figure 1: 
(See also, LIT_ALL_PeakPositions.csv)
* ~1.7 mM Octadecanoic acid on H2O pH 9 symmetric and asymmetric stretches were extracted from reference (26) which utilized IRRAS at 294 K on surface layers with 0.202-0.333 nm2/molecule. The COO sym is listed as a split band 1404 and 1423 cm-1. The latter was not plotted as it comes from a coupling between the COO sym and and methylene bend. The COO asym is given as a split band with ranges 1558-1562 and 1542-1546 cm-1. We averaged the outer limits of these ranges to get 1552 cm-1.
*1.7 mM Octadecanoic acid on 1 mM CaCl2 in H2O pH 6 symmetric and asymmetric stretches were extracted from reference (27) which used IRRAS at 294 K to interrogate Octadecanoic acid spread to 0.192-0.333 nm2/molecule. The asymmetric stretch is given as two peaks 1565 and 1542 cm-1 which we averaged to get 1554 cm-1.
* The 0.86 mM hexacosanoic acid on pH 12 H2O symmetric stretch was extracted from reference (28) which used SFG. The asymmetric peak began to appear at pH 10.5 and monolayer nearly fully ionized at pH 12.
* 5mM d32-Arachiadic acid on 3.1 mM CaCl2 in pH 8.8 (total deprotonation) H2O symmetric and asymmetric stretches were extracted from reference (29) which used PM-IRRAS at the surface pressure 25 mN/m.
* The H2O (liquid) water bend was extracted from reference (30) which utilized attenuated total reflectance IR spectroscopy.
* Sodium acetate (saturated) in H2O and D2O symmetric and asymmetric stretches were extracted from reference  (31) which used IR spectroscopy of a bulk saturated solution of H2O and D2O.
* Lithium phenyl acetate symmetric and asymmetric stretches were extracted from reference (32) which used gas-phase UV and conformer resolved IR.

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