Correlation structure/IR-spectroscopic properties of the dipeptide L-phenylalanyl-Lalanine dihydrate (H-Phe-Ala-OHź2H2O) and its hydrochloride (H-Phe-Ala-OHźHCl) in solid-state is elucidated by means of the linear-polarized IR- (IR-LD) spectroscopy of oriented colloid suspension in nematic host. The IR-spectroscopic and structural assignment obtained by the polarization tool is compared with known crystallographic data of H-Phe-Ala-OHź2H2O. The characterization of the hydrochloride salt is supported in addition by the HPLC tandem ESI mass spectrometry (MS/MS), 1H- and 13C-NMR, TGA and DSC methods. Quantum chemical calculations are performed with a view to obtain electronic structure and vibrational properties of both neutral and protonated dipeptide, thus completing the experimental assignment.
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Linear-dichroic infrared spectra (IR-LD) of 3-ethoxy-4-(N-norcodeino-)cyclobutene-1,2-dione (1) and codeine dihydrogenphosphate (Codeinum phosphoricum) (2), oriented as solid suspensions in nematic liquid crystals, have been measured. IR characteristic band assignments were made, and used in stereo-structural predictions. The results were compared with crystallographic structures of similar organic systems, and found to be in good agreement.
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The applications of linear-polarized IR-spectroscopy to oriented colloid suspensions in a nematic host are demonstrated with croconic and rhodizonic acids. The experimental IR vibrational assignments of the solid-state of both neutral compounds are presented. Assignments are supported by theoretical quantum chemical calculations and vibrational analysis at the DFT level of theoretical approximation with the 6-311++G** basis set. [...]
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