NMR Spectroscopy Data Acquisition - Christian Schorn.pdf - medicalheaven_radiology - ldfg

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Preface

The application of NMR spectroscopy into new fields of research continues on an

almost daily basis. High-resolution NMR experiments on compounds of low molecular

mass in the liquid phase are now routine and modern NMR spectroscopy is aimed at

overcoming some of the inherent problems associated with the technique. Thus higher

magnetic field strengths can be used to help overcome the problems associated with low

sample concentration enabling the analysis of complex spectra of large macromolecules

such as proteins whilst also helping to advance the study of non liquid samples by MAS

and solid state NMR spectroscopy. Apart from the chemical and physical research fields

NMR spectroscopy has become an integral part of industrial production and medicine,

e.g. by MRI (magnetic resonance imaging) and MRS (magnetic resonance spectroscopy).

The basic principles of acquiring the raw time domain data, processing this data and then

analysing the spectra is similar irrespective of the particular technique used. The

diversity of NMR is such that a newcomer to NMR spectroscopy might train in the field

of high resolution NMR and establish his career in solid state NMR. A distinct advantage

of NMR spectroscopy is that the basic knowledge of acquisition, processing and analysis

may be transferred from one field of endeavour to another. These ideas and perspectives

were the origin for the series entitled Spectroscopic Techniques: An Interactive Course .

The section relating to NMR Spectroscopy , consists of four volumes

•

Volume 1 – Processing Strategies

•

Volume 2 – Data Acquisition

•

Volume 3 – Modern Spectral Analysis

•

Volume 4 – Intelligent Data Management

and deals with all the aspects of a standard NMR investigation, starting with the

definition of the structural problem and ending – hopefully – with the unravelled

structure. This sequence of events is depicted on the next page. The central step is the

transformation of the acquired raw data into a NMR spectrum, which may then be used

in two different ways. The NMR spectrum can be analysed and the NMR parameters

such as chemical shifts, coupling constants, peak areas (for proton spectra) and

relaxation times can be extracted. Using NMR parameter databases and dedicated

software tools these parameters may then be translated into structural information. The

second way follows the strategy of building up and making use of NMR databases. NMR

spectra serve as the input for such data bases, which are used to directly compare the

measured spectrum of an unknown compound either with the spectra of known

compounds or with the spectra predicted for the expected chemical structure. Which of

Preface

the two approaches is followed depends on the actual structural problem. Each of them

has its own advantages, limitations and field of application. However, it is the combined

application of both techniques that makes them such a powerful tool for structure

elucidation.

The contents of volumes 1 – 4 may be summarized as follows:

Volume 1: Processing Strategies

Processing NMR data transforms the acquired time domain signal(s) – depending on

the experiment – into 1D or 2D spectra. This is certainly the most central and important

step in the whole NMR analysis and is probably the part, which is of interest to the vast

majority of NMR users. Not everyone has direct access to an NMR spectrometer, but

most have access to some remote computer and would prefer to process their own data

according to their special needs with respect to their spectroscopic or structural problem.

This also includes the graphical layout for the presentation of reports, papers or thesis. It

is essential for the reliability of the extracted information and subsequent conclusions

with respect to molecular structure, that a few general rules are followed when

processing NMR data. It is of great advantage that the user is informed about the many

possibilities for data manipulation so they can make the best use of their NMR data. This

is especially true in more demanding situations when dealing with subtle, but

nevertheless important spectral effects. Modern NMR data processing is not simply a

Fourier transformation in one or two dimensions, it consists of a series of additional steps

in both the time and the frequency domain designed to improve and enhance the quality

of the spectra.

Processing Strategies gives the theoretical background for all these individual

processing steps and demonstrates the effects of the various manipulations on suitable

examples. The powerful Bruker 1D WIN-NMR, 2D WIN-NMR and GETFILE software

tools, together with a set of experimental data for two carbohydrate compounds allow

you to carry out the processing steps on your own remote computer, which behaves in

some sense as a personal “NMR processing station”. You will learn how the quality of

NMR spectra may be improved, experience the advantages and limitations of the various

processing possibilities and most important, as you work through the text, become an

expert in this field. The unknown structure of one of the carbohydrate compounds should

stimulate you to exercise and apply what you have learnt. The elucidation of this

unknown structure should demonstrate, how powerful the combined application of

several modern NMR experiments can be and what an enormous and unexpected amount

of structural information can thereby be obtained and extracted by appropriate data

processing. It is this unknown structure which should remind you throughout this whole

educational series that NMR data processing is neither just “playing around” on a

computer nor some kind of scientific “l’art pour l’ art”. The main goal for measuring and

processing NMR data and for extracting the structural information contained in it is to

get an insight into how molecules behave. Furthermore, working through Processing

Preface

VII

STRUCTURAL PROBLEM

EVALUATION OF EXPERIMENTS

AND DATA ACQUISITION

Volume 2: Data Acquisition

RAW DATA

DATA PROCESSING

Volume 1: Processing Strategies

SPECTRA

DATA ANALYSIS

DATA ARCHIVING

Volume 3: Modern Spectral Analysis

Volume 4: Intelligent Data Management

NMR-PARAMETER

NMR DATA BASE

DATA INTERPRETATION

DATA MANAGEMENT

Volume 4: Intelligent Data Management

MOLECULAR STRUCTURE

NMR Spectroscopy Data Acquisition - Christian Schorn.pdf

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