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Title: Experimental (spectroscopic) and theoretical studies of rhodanine (2-Thio-4-Oxothiazolidine) and its derivatives
Author: Jabeen, Saima
ISNI:       0000 0004 2737 6307
Awarding Body: University of Greenwich
Current Institution: University of Greenwich
Date of Award: 2007
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There is paucity of data in the scientific literature pertaining to detailed assignments of the vibrational spectra of nitrogen containing thiocarbonyl compounds. Herein, three five membered heterocyclic compounds –rhodanine, 3-aminorhodanine, and 3-methylrodanine-containing both amide and thioamide moieties have been investigated from both an experimental and theoretical perspective. Experimental Raman (?o = 632.8 nm) and infrared spectra of the three compounds have been recorded in the solid state (protonated and deuteriated). Deuteriation studies revealed that not only are the protons attached to the nitrogen atom labile, but the protons of the active methylene group also undergo hydrogen-deuterium exchange. Comparisons of protonated and deuteriated spectra enable discrimination of the bands associated with N-H, NH2, CH2 and CH3 vibrations. Ab initio calculations, using density functional theory (DFT; B3-LYP) employing the cc-pVTZ basis set, have been conducted in order to obtain the geometry optimized, energy minimized structures of the isolated molecules in the gas phase. The data generated was then used to (a) compare, where possible, the calculated structure with the experimentally determined X-ray crystallographic structure, and (b) carry out normal coordinate analysis in order to obtain the potential energy distributions (PEDs) of each normal vibrational mode thus allowing detailed vibrational band assignments for the three molecules. The assignment of the bands associated with the amide and thioamide groups have been made possible by comparing the spectra of the three molecules and DFT calculations. In the case of rhodanine, the cis amide I mode is attributed to the bands at ~1713 and 1779 cm-1, whereas a band at ~1457 cm-1 is assigned to the amide II mode (Raman and IR). The vibrational bands for the thioamide II and III modes of rhodanine, 3-aminorhodanine, and 3-methylrhodanine are observed at 1176 and 1066/1078; 1126 and 1044; 1107 and 984 cm-1 in the Raman and 1187 and 1083; 1230 and 1074; 1116 and 983 cm-1 in the IR spectra, respectively. Surface enhanced Raman spectroscopy (SERS) studies of the three molecules have been conducted as a function of pH, concentration, and time in order to understand their interaction/absorption behaviour with citrate-reduced Ag and Au colloidal (substrate) nanoparticles, as well as for semi-quantitative trace analysis. The pH studies revealed that the optimum conditions for SERS analysis is the presence of HC1 and poly(L-lysine) at pH 2.3 (?o = 632.8 nm). The SERS studies also revealed the presence of a strong band at 1566/1575/1572 cm-1 (for rhodanine, 3-aminorhodanine and 3-methylrhodanine, respectively), irrespective of experimental conditions used.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; QD Chemistry