X-Ray Absorption Fine Structure (Xafs) Studies Of Some Copper Compounds And Complexes Of Biological Importance
Creators: name: Gaur, Abhijeet
Publisher: name: Zenodo
Year: 2012

description: In the present thesis, the X-ray absorption fine structure (XAFS)spectroscopy has been used to study copper compounds and complexes. Studies have been done using both EXAFS and XANES spectroscopies. Basically, following two types of studies have been made.
Firstly, EXAFS study at the K-edge of copper in mixed ligand copper complexes of biological significance have been done to yield useful and important information about the molecular structure of the complexes which are mononuclear,
binuclear as well as trinuclear.
Secondly, an evaluative and comparative study of the different methods of speciation using XANES at the K-edge of copper have been done by taking several mixtures of copper compounds and complexes.
The thesis is divided in ten chapters.
Chapter I is introductory in nature and describes the basic phenomenon of absorption of X-rays. The terms used in the X-ray absorption spectroscopy have been explained. Theory of EXAFS has been given in brief and the method of extracting structural parameters has been outlined. It has been pointed out that XANES can be used to extract information about the oxidation state, three dimensional geometry, and coordination environment of elements under investigation and that the parameters determined by XANES and EXAFS relate to
the local environment surrounding the absorbing atom. The reasons for choosing the five series of mixed ligand complexes of copper studied in this thesis using EXAFS
(in chapters IV to IX) have been outlined. The use of XANES has been discussed, specially in speciation. It has been shown that by taking standards of well-defined chemical species, analysis of XANES can be used to determine metal speciation, i.e., determination of the chemical forms along with the relative quantity of the different species in a given sample. The need for making a comparative study of the
different methods of speciation (in chapter X) has been outlined.
Chapter II gives the experimental details. The copper complexes studied in this thesis have been prepared by Dr. Jagdish Prasad and Dr. Krishna Srivastava at the Department of Chemistry, Allahabad University, Allahabad. The absorption screens have been prepared by the author following standard methods at RRCAT, Indore. The details of the four EXAFS beamline at four different synchrotron
facilities, where the X-ray absorption spectra have been recorded, are described in this chapter. The copper K-edge EXAFS spectra of the complexes studied in chapters IV, VII and IX have been recorded at the BL-8 dispersive EXAFS
beamline at 2 GeV Indus-2 synchrotron source at Raja Ramanna Center for Advanced Technology (RRCAT), Indore, India. The copper K-edge XAFS spectra of the copper complexes studied in chapter V, VI and VIII were recorded at EXAFS
beamline 11.1 at ELETTRA Synchrotron Light Laboratory, Basovizza, Italy. The copper K-edge XAFS spectra of the copper compounds and their mixtures studied in
chapter X were recorded at three EXAFS beamlines, namely, (1) EXAFS beamline X-19A at National Synchrotron Light Source (NSLS), Brookhaven National Laboratory, Upton, New York, USA, (2) EXAFS beamline 11.1 at ELETTRA Synchrotron Light Laboratory, Basovizza, Italy and (3) EXAFS wiggler beamline 4–1 at the Stanford Synchrotron Radiation Laboratory (SSRL), Stanford, California, USA.
In chapter III, the method of calibration of BL-8 dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at Raja Ramanna Center for Advanced Technology (RRCAT), Indore, India has been outlined (Gaur et al., 2011, Johari, 2011). A comparative study of the EXAFS spectra recorded at this beamline with those recorded at three other well known synchrotron EXAFS beamlines has been done in order to evaluate the quality and reliability of the recorded data and the usefulness of this beamline. It has been demonstrated that the results obtained from the EXAFS spectra recorded at this beamline are comparable to those obtained from other synchrotron EXAFS beamlines. This attempt appears to be the first in this direction.
Chapters IV-VIII describe the results of XAFS study at the K-edge of copper in five different series of copper complexes. The studied copper complexes are
interesting from the point of view of analysis of the EXAFS spectral data. First series has binuclear monohydroxo-bridged and dihydroxo-bridged copper(II) complexes. Second series has copper(II) mixed ligand complexes, having analogous structures. Third series has Schiff-base mononuclear and binuclear copper(II) salen/salophen complexes. Fourth series has mixed ligand copper(II) complexes having different coordination environments and geometries. Fifth series has copper (I) thiourea complexes having different types of coordination environment. In
chapter IX, a trinuclear Schiff-base copper complex in which three metal sites are present, has been studied.
Chapter X gives the details of work done on speciation. The different methods of speciation have been described in detail. The objective of the present work is to make a comparison of the different methods of speciation by taking
several examples of mixtures of Cu(I) and Cu(II) compounds. Four different types of studies have been done for this purpose.
The present work represents a transition from laboratory based experiments to highly technological synchrotron based experiments, from X-rays from X-ray tubes to X-rays from synchrotrons and from semi-empirical and qualitative analysis of the X-ray absorption data to its quantitative analysis. The work has been done at four different beamlines at four synchrotron facilities. In India, the work has been
done on recently developed Indus-2 synchrotron facility which was not earlier available to Indian workers. For the last forty years research workers in our laboratory were doing experiments on laboratory set-ups. Now, it is hoped that future research workers not only from our laboratory but also from other Indian laboratories will do experiments on synchrotrons. Hence, details regarding experiment and analysis of the XAFS data have been given at the appropriate places in the thesis so that any body who wants to start research work in the field of XAFS may get necessary information at one place. I consider this as important because the beamtime at EXAFS beamline at Indus-2 synchrotron facility may easily become available to Indian workers which was not available uptil now. This record was migrated from the OpenDepot repository service in June, 2017 before shutting down.