Supporting Information Testing the potential of the ferrocene chromophore as a circular dichroism probe for the assignment of the screw-sense preference of tripeptides

A combined strategy utilizing experimental (infrared, nuclear magnetic resonance, circular dichroism, X-ray) and computational (time-dependent density functional theory) techniques is illustrated o...


Single crystal X-ray crystallography
A single crystal was mounted on a glass fiber. Data collections were carried out on an Oxford Diffraction Xcalibur four-circle kappa geometry single-crystal diffractometer with Sapphire 3 CCD detector, using a graphite monochromated MoKα ( = 0.71073 Å) radiation, and applying the CrysAlisPro Software system [1] at 293(2) K. Data reduction, including absorption correction, was done by CrysAlisPro program.
The structures were solved by the Superfilp computer program. [2] The coordinates and the anisotropic thermal parameters for all non-hydrogen atoms were refined by full-matrix least-squares methods based on F 2 using the SHELXL program. [3] The hydrogen atoms were generated geometrically using the riding model with the isotropic factor set at 1.5 Ueq.
Graphical work has been performed by Mercury 4.3.1. [4] The thermal ellipsoids were drawn at the 30 % probability level. General and crystal data with the summary of intensity data collection and structure refinement for compound 2a are given in Table S3. CCDC 2035760 contains the supplementary crystallographic data for this paper.

S42
DFT study Table S8. Relative energies of the most stable conformers of compounds 1a-4a optimized in chloroform at 298 K. Optimizations performed at the B3LYP-D3/6-311+G(d,p), LanL2DZ for Fe level of theory, PCM model for modelling solvent effects. Proline puckering modes of both prolines (Pro1 is closer to N-terminus), cis/trans isomers of proline peptide bonds, helicity, labels of intramolecular hydrogen bond patterns displayed in Figure S35 and X-Y distances [Å] of the selected X-H···Y hydrogen bonds connecting the n-membered rings.  Figure S39. The hydrogen bond patterns observed in the optimized geometries of the most stable conformers 1a -4a. Numbering scheme for the selected n-membered hydrogen bonded rings. Figure S42. Superposition of the calculated (2a-5, blue colour) and experimentally determined (from the crystal structure, orange colour) geometries of compound 2a. RMSD is 0.9489 Å. Figure S43. TDDFT calculated ECD spectra of compounds 1a -4a. The final Boltzmann-averaged spectrum at 298 K (red dashed line) is obtained by weighting each conformer spectrum (coloured solid lines) with the appropriate conformer Boltzmann weight factor for the final set of structures labeled in Table S6.

Excited states
Compound 1a Excited states 1 to 6 in the 1a-1 conformer. Left side displays pairs of natural transition orbitals and occupation numbers (above arrows) particular to the states of interests. Right side shows density difference plot for each transition, regions of increased (violet) and decreased (cyan) electron density. Figure S44. Excited states 1 in the 1a-1 conformer. Figure S45. Excited states 2 in the 1a-1 conformer. Figure S46. Excited states 3 in the 1a-1 conformer. Figure S47. Excited states 4 in the 1a-1 conformer.

S51
Compound 2a Excited states 1 to 6 in the 2a-1 conformer. Left side displays pairs of natural transition orbitals and occupation numbers (above arrows) particular to the states of interests. Right side shows density difference plot for each transition, regions of increased (violet) and decreased (cyan) electron density.