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Author Sarkar, Jyotirmoy
Source IACS Kolkata
Content type Text
Educational Degree Doctor of Philosophy (Ph.D.)
File Format PDF
Language English
Subject Domain (in DDC) Natural sciences & mathematics
Abstract The thesis entitled "A Combined experimental and theoretical investigation on the Surface Enhanced Raman scattering of some organic molecules adsorbed in metal hydrosol" comprises of eight chapters. This focuses on the present dissertation is to investigate the structure, orientation, conformation, binding mechanism and reactivity of some organic molecules adsorbed on nano colloidal silver surface using FTIR, NRS and SERS technique. The contents of the thesis are given below.Chapter 1 contains the general introduction with a brief review of the relevant parts of existing theories employed in this work to interpret the experimental results.Chapter 2 discusses the methods of sample preparation, purification and various experimental techniques of NRS, SERS, and FTIR.Chapter 3 deals with the detail experimental and theoretical NRS, SERS and FTIR spectra along with a tentative vibrational assignment of the observed bands of the biologically important, 2-aminobenzothiazole (2-ABT) molecule. The optimized structural parameters and the computed vibrational wavenumbers of the compound have been estimated from ab initio HF and DFT calculations. Some vibrational modes of the molecule have been reassigned. The adsorptive behavior of 2-ABT on a colloidal silver surface at different adsorbate concentrations, close to that encountered under physiological conditions in living systems has been elucidated from the SERS spectra. NRS spectra of the chemically prepared 2-ABT-Ag(I) complex and their comparison with the SERS spectra are also reported herein.Chapter 4 presents the detail experimental and theoretical NRS, SERS and FTIR spectra along with a tentative vibrational assignment of the observed bands of the 2-Amino-4-Methyl Benzothiazole (2-AMBT). The adsorptive behavior of these molecules on the colloidal silver surface at two different adsorbate concentrations recorded in different time domains have been elucidated from the SERS spectra. The silver surface may serve as an analogue for the artificial biological interface. The experimentally observed SERS spectra are compared with the theoretically modeled 2-AMBT-Ag (I) surface complexes using ab initio RHF and DFT calculations. Themost favorable adsorptive sites of the 2-AMBT molecule have been estimated by natural population analysis (NPA) using the above-mentioned high level of theories.Chapter 5 discusses the studies on the experimental and theoretical NRS, SERS and FTIR of 2-Amino-6-methylbenzothiazole (2A-6MBT) molecule. The adsorptive behavior of 2A-6MBT molecules on the colloidal silver surface at different adsorbate concentrations has been elucidated from the SERS spectra. In these investigations, the silver surface may serve as an analogue for artificial biological interface, and after elucidating the adsorption mechanism of the molecule; the study can be extended to the adsorption on membranes or other interesting biological surface for medical or therapeutic treatments. DFT calculations on models of 2A-6MBT-Ag0 and 2A-6MBT-Ag+ surface complexes are also reported herein.Chapter 6 reports the adsorptive behavior of Rh123 on the colloidal silver surface and the nature of charge transfer between the molecule and the metal using FTIR and SERRS spectra together with ab initio and DFT calculations. This study may be helpful to understand the role of this molecule at biological interfaces.Chapter 7 deals with the detailed experimental and theoretical normal Raman spectra (NRS), SERS and FTIR spectra of 4-Methyl-4H-1, 2, 4-Triazole-3-Thiol (4-MTTL) molecule. From a more fundamental point of view, 4-MTTL is also very interesting compound because of its probable existance in thione-thiol tautomeric equilibrium in electronic ground state. The pH dependent NRS spectra of the molecule in aqueous solution have been recorded to elucidate the protonation effect and preferential exitence of the tautomeric form/forms of the molecule in acid, neutral and alkaline media. The adsorptive behavior and the orientation of the molecule on the nanocolloidal silver surface at various pH values are also recorded herein.Chapter 8 reports the results of the investigation on the concentration-dependent SERS study of the biologically important, 2ATH molecule, adsorbed on silver nanocolloids is described and compared with its FTIR and NRS spectra in varied environments. The optimized structural parameters, preferential existence and computed vibrational frequencies of the tautomeric amino and the isomeric imino forms of the molecule in the gas phase and in methanol solvent have been estimated from the DFT calculations. The observed Raman signals along with the corresponding FTIR bands have been assigned and presented for the first time from the potential energy distributions (PED) in terms of internal coordinates of the molecule estimated from the results of DFT calculations. The adsorptive behavior and adsorptiongeometry of the preferred tautomeric form/forms of the molecule on nanocolloidal silver surface at different adsorbate concentrations, close to that encountered under physiological conditions in living systems have been elucidated from the SERS spectra.
Education Level UG and PG
Learning Resource Type Thesis