Vibrational spectra of bis(L-ornithinium) chloride nitrate sulfate

Abstract

The Raman and infrared absorption spectra of 2(C 5 H 14 N 2 O 2 2+ )·Cl − ·NO 3 − ·SO 4 2− crystal containing three anions were recorded at room temperature and were interpreted in the light of crystal structure data. The presence of a carbonyl group was identified. The carboxylic group was found to exist as COOH. The formation of O -H· · ·O, N -H· · ·O and N -H· · ·Cl asymmetric hydrogen bonds contributes considerably to the crystal cohesion and is responsible for the changes in the position and intensity of several bands. The vibrational spectra show that the anions were found to coordinate through hydrogen bonding interactions to other ligands in the crystal. The lattice wavenumbers of the halide radical (chlorine anion) were also assigned in terms of hydrogen bond vibrations.

Surface enhanced Raman scattering and quantum‐mechanical calculations on self‐assembling oligopeptides

“…Other bands typical of the peptidic bond, enhanced in the SERS spectrum, lie at 760 (Amide V, weak) and 655 cm −1 (Amide IV) . This latter vibration arises mainly from an OC–NH bending mode and is expected to be enhanced only if the group is not parallel to the surface . Optimized geometries of Ag 2 interacting with the amide group (Tables and S1–S3) showed a tilted dihedral angle between Ag and the amide plane ranging from 100° to 126°.…”

“…The SERS spectra of all the investigated peptides, normalized to the water ν OH band at 3,200-3,400 cm −1 , are shown in Figure 1, and the assignments of the bands observed in the SERS and Raman spectra are reported in Tables 2, 3. In general, the most important feature of the SERS spectra of all the studied peptides is that the peptidic backbone is not intensified in the spectra δ NH 3 + (Lys) [25] 1,579 sh 1,579 sh 1,579 sh 1,575 m δ NH 3 + (Lys) [28] 1,556 vw 1,530 sh 1,544 sh 1,549 vw 1,535 sh ν as COO - [6][7][8] Amide II [8] δ NH 3 + (Arg) [34] 1,508 sh 1,514 sh Amide II [32,35,36] δ CH 2 [7,8,25,26,32,37,38] [42] Amide III [7,8,25,26] 1,253 br 1,258 br 1,251 w ω CH 2 [37] Amide III [7,8,25,26] 1,246 m 1,245 m ω CH 2 [37] τ C α2 H 2 [7,26] 1,232 m ν as C α CN [7] 1,157 w 1,160 w 1,157 w 1,153 m τ CH 2 (Lys) [26] ν CN (Arg) [7] ν CC [26] 1,125 w 1,124 w 1,129 w τ HNC [6,31] 25,27,31,32,35] 1,100 m 1,098 m 1,115 m ν CC [26,…”

“…ν CC [7,8,25,26] 889 w 882 sh 882 sh --τ HCCN [8] ν CC [26,29] 817 w 816 vw 822 vw 815 w τ HCCO [31] Amide V [26] 760 w 758 vw 756 br 770 w τ HCCC [29] Amide IV [7] 640 vw 655 br 658 br 654 vw 657 w δ COO - [29,31,32] ω COO - [8,25,26,30,37] 600 vw 603 vw 613 vw…”

“…However, a different orientation of the "scrambled" peptide with respect to the Ag surface can be deduced by the disappearance of the lower wavenumber bands due to δ COO − (about 650 cm −1 ) and ω COO − (560 cm −1 ), visible in the SERS spectra of pept1 and pept2. [7] ν CC [40] ν CC [29] 1,058 w 1,043 w τCH 2 [29] ν 18a [34] 1,020 m ν CC [25] 938 vw 937 w ν C-COO - [6,8,30,37] Fermi resonance [8,25,31,34,37] 856 s; 829 s 854 s; 832 m Amide V [26] 773 w Amide IV [7] 668 vw ν 6b [7,8,25,34] 644 s 645 m ω COO - [8,25,26,30,37] 600 w 613 m Amide VI [7,8,26] ρ C¼O [33] 555 vw 564 vw ρ C¼O [27] 540 vw ω COO - [7,30] τ NH 3 + [32] 480 w Note. SERS = surface-enhanced Raman scattering.…”

“…[7,25] This latter vibration arises mainly from an O¼C-NH bending mode and is expected to be enhanced only if the group is not parallel to the surface. [32,47] Optimized geometries of Ag 2 interacting with the amide group (Tables 4 and S1-S3) showed a tilted dihedral angle between Ag and the amide plane ranging from 100°to 126°. A similar behavior was observed in pept2 ( Figure 3 and Table 2).…”