Explaining the trends of Nuclear Shielding caused by Magnetic moments related to Susceptibilties Copy

Dr. S. Aravamudhan

A selfie clicked at Ashiana Shuhan 2BHK residence, (outer) Chennai, tamil Nadu

The present subject of research has inception at the instance which made a breakthrough in the explanations of discrepancies repeatedly encountered while trying to account for the results of experimental proton shielding tensor measurements by the Multiple Pulse Selective Averaging methods in Solid State
NMR. This work ,particularly on the single crystals of Pyromellitic Acid Dianhydride, opened up -as was pointed out in the Discussions of the published paper ( S. Aravamudhan, U.Haeberlen, H.Irngartinger & C. Krieger, Mol. Phys. Vol. 38, P 241, Year 1979)-two pronged investigation of the consequences:
1) To study the possibilities of calculating INTRA (in exclusion of
the INTER) molecular contribution to the shielding tensors as arising due to the induced fields by simple point dipole contributions. (Such a calculation would require approriate sets of Susceptibility tensor values which in the paper above were obtained from Flygare's data - Click &Jump to remark below - and such choices of empirical data for calculation of other physical quantities would be beset with ambiguities as also pointed out at the "discussion" of the publication by Aravamudhan et. al.) And 2) to find methods of extending the considerations of intermolecular calculations to the whole macroscopic extent of the specimen instead of the only semi-microscopic (of about 100 Angstroms extent) elements.These should enable the simple basis of dipole contributions to be understood more comprehensively from the intra- to intermolecular consequences without the acompanying obscurities due to the involved mathematical procedures which render all the explanations to be beset with a kind of abstractness which causes discomfitures while applying in Chemical contexts.
On the aspect (1)a poster presentation could result at the Joint ISMAR-CA'98 held at the Techniche Hochlue Berlin in 1998. The aspect (2) above is the matter dealt with in the presentation at the 2nd Alpine Conference on Solid State NMR,Chamonix Mont-Blanc,France during 9-13 Sept.2001 .
All these aspects have been presented (in steps) at the annual Symposia of the National Magnetic Resonance Society,INDIA
Hence the present achievement is founded firmly on the results of the work as Post Doctoral Fellow during 1975-77,and the informations gathered by literature survey while being at the NCL,Pune and the further supplementary assistance available in obtaining published reference materials from CSIR labs.The earlier efforts to realise were all in the form of several M.Sc.,Project Works(each of only six months duration) at the NEHU,Chemistry. A great deal remains to be inferred by intensive efforts and communicate them as publications in Journals. The possible applications of these simple calculation procedureshave beenpointed out broadly in the poster presentation at the XIII Internatinal Biophysics Congress in held in New Delhi in September 1999 and this participation was supported by an INSA grant. The research results which are contained in the presentations are all the outcome of the work carried out during the tenure of appointment as teacher in the Department of Chemistry , North Eastern Hill University, Shillong. The results are being further pursued with the purpose of finalising them for publication in refereed Journals.Most of the efforts had been resulting only in a single author presentations.The publication includes an earlier Presentation in XIII International Biophysics Congress and related Biopysical & Biochemical meetings.1]. The copy of the ABSTRACT uploaded & submitted at the Webabstract Submission box/page of the XIV I.B.C. is being included in these pages. A grant could forthcome form the organizers of the 2nd Alpine Conference on SSNMR for the participation.

S.Aravamudhan
Author of the Contribution to XIV I.B.C
Lecturer,Department of Chemistry, North Eastern Hill
University, Shillong,Meghalaya,India

The following is the essential features on the basis of which an application to the University Grants Commission,New Delhi was sent in the year 1981 for the grant of a Research Associateship to enable computations at I.I.T.Madras but evenbefore any considerations by the UGC an appointment as Lecturer at NEHU made it possible to keep continue the studies. An effort was also taken to work out a viable Ph.D., thesis research proposal of this subject which would have fetched a degree to a capable student at the University

Description  Highlighting  the above context for inferring more.
Describtion of  Recent Efforts  with theoretical tools, for accessibility and viability of adequate approaches.

 DETERMINATION AND APPLICATIONS OF CONTRIBUTIONS TO SHIELDING TENSORS
 

Shielding tensor contributions can be obtained by experimental NMR studies on solid samples and from theoretical Calculations(1,6).Since it enables  the determination of the principal values for the shielding tensor rather than just the trace of the tenosr, this information is more detailed than that obtained from NMR experiments involving the liquid state and thus provides more information on the chemical environment(2).Applying these methods (mentioned in references 1&2) to ring current contributions to shielding tensors could provide valuable additional information to what is already available(3).Such attempts could lead to further information on possible NMR experiments(in liquids and solids)on macromolecules which could supplement informations available from x-ray crystallography(3). Since some of the methods of obtaining the shielding tensor informations are related to different aspects of magnetic susceptibility anisotropy values, such study could provide a possible method for obtaining consistent sets of bond- and atom- susceptibility anisotropy values(4). The methods used for calculating shielding tensor contributions (using susceptibility anisotropy values) could be extended to calculate demagnetizing factors in magnetic materials(5). It is proposed to carry out detailed studies on obtaining such shielding tensor informations to be able to obtain information on chemical structures and certain physical properties.
References: 1. U.Haeberlen, "High Resolution NMR in Solids: Selective Averaging", Advances in Magnetic Resonance,Supplement 1, Academic Press (1976).   2.N.R.Jagannathan, S.S.Rajan and E.Subramanian, Current Science, Vol.63, page 743 (1972).  3.Stephen J.Perkins,"Application of Ring Current Calculations to Proton NMR of Proteins and trans RNA", in 'BIOLOGICAL MAGNETIC RESONACE', Vol.4, page 193, Edited by Lawrence J.Berliner & J.reuben, Plenum Press (1972). 4. W.H.Flygare, Chemical Reviews, Vol.74, page 653 (1974).

In this reference Flygare et al., report that a set of bond (tensor)susceptibilites derived by an empirical fit from the set of TOTAL (experimentally determined) MOLECULAR SUSCEPTIBILITY TENSOR values and a set of atom (tensor) susceptibilities were derived by an empirical fit from the same set of TOTAL MOLECULAR TENSOR VALUES. Further, the set of Bond susceptibities thus derved could not be constructed from the similarly derived atom susceptibilities. This points out that two empirically derived consistent sets are not mutually consistent. This requires an expalanation on theoretical grounds. return to Aravamudhan et.al., above. 

5. Project Report submitted to the Department of Chemistry,North Eastern Hill University (in partial fulfilment of the requirements of the Degree of Master Of Science) by Debashish Dutta(1993),Sushmita Dhar (1994) and K.Yhom (1996). 6. M.Mehring, "High Resolution NMR in Solid",Springer,Berlin (1983).

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