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Book Review Applications of Mass Spectrometry to Organic Stereochemistry. (Series Methods in Stereochemical Analysis.) Edited by J. S. Splitter and F. Turecek

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cerned with a lipid-binding protein, which
serves to illustrate and summarize the
contents of the preceding seven chapters.
Chapter 9 contains an excursion into software for displaying and manipulating
molecular models.
The text is written in a fluent style and
can be quickly understood even by nonspecialists. The few mathematical formulas included are essential for describing
the relationships involved, and the figures
are instructive and well chosen. The book
entirely fulfills its aim of providing a
bridge between molecular biologists and
biochemists on the one hand and protein
crystallographers on the other, and I
recommend it to everyone who is concerned with molecular structures. The
brevity of the text and the high standard
of presentation (“crystal clear”) make this
a very suitable book to use as an accompaniment to practical sessions or as an
introductory course in protein cryst a I logra p h y .
Wolfram Saenger
lnstitut fur Kristallographie
der Freien Universitiit Berlin (FRG)
Applications of Mass Spectrometry to
Organic Stereochemistry. (Series :
Methods in Stereochemical Analysis.) Edited by J. S . Splitter and F.
Turepek. VCH Verlagsgesellschaft,
Weinheim/VCH Publishers, New
York, 1994. 705 pp., hardcover
DM 198.00, $ 125.00.-ISBN 3-52726525-2/0-89573-303-X
Review articles on mass spectrometric
studies of stereoisomeric compounds have
appeared at irregular intervals over a period of many years, extending from Meyerson and Weitkamp (1968) through Green
(1976, 1978) and Mandelbaum (1977,
1983) up to Turetek (1 987). With the publication of this book we now have a comprehensive survey of the field. Twenty
well-known authors have contributed articles on 22 topics, covering published
work up to 1992. The ability to solve stereochemical problems is certainly not regarded as one of the particular strengths
of mdSS spectrometry, but despite this
there exists a surprising wealth of examples where stereochemical differences
are clearly reflected in mass spectra. This
applies even under the conditions of 70 eV
electron impact ionization, which results
in the transfer of a large amount of surplus energy, typically 2- 10 eV. The likelihood of being able to distinguish between
stereoisomers is intrinsically greater if the
conversion to the gas phase and the subsequent ionization are carried out under
conditions that minimize the excitation of
the molecules. This can be achieved by
suitable modifications to the instrumental
conditions, such as cooling the ion source,
the use of low voltage electron impact ionizaion, or substituting more gentle ionization processes such as photoionization,
electric field ionization, or chemical ionization.
A short introductory chapter on the
techniques of mass spectrometry (author:
Falik) is followed by chapters dealing
with the structures of ions and the influence of stereochemistry on the mass spectra of acyclic molecules (Splitter). Further
chapters discuss the behavior of stereoisomeric cyclic compounds (Eadon, Valente,
TureEek, Grutzmacher, Vekey, Mandelbaum, Groenewold, Gross). In these compounds the ring structure limits the number of conformers that can exist, and there
is then the possibility that this reduced
mobility may result in stereospecific rearrangements causing differences in the
mass spectra which can be interpreted.
Using model compounds as examples, the
authors describe in detail the most important types of phenomena, including enthalpy effects, “hidden” stereochemistry,
effects of conformational changes, steric
effects influencing the accessibility of hydrogen atoms for rearrangements, stabilization of cdrbocations by neighboring
groups, retro-Diels-Alder fragmentations, and examples of the use of field ion
kinetics (FIK) and mass-analyzed ion kinetic energy release (MIKE) measurement
techniques.
A very informative chapter o n the use
of chemical ionization (Winkler, Splitter)
describes results obtained with E,Z-isomeric olefins, and, in greater detail, cyclic
compounds. By choosing appropriate reactant gases in the chemical ionization
method it is possible to optimize specific
fragmentation processes and/or adduct
formation for the system under investigation. A separate chapter (Houriet,
TureEek) is devoted to the study of stereochemical effects in an ion cyclotron resonance mass spectrometer, a type of instrument uniquely suited for investigating
ion-molecule reactions. This technique
yields information about the long-term
behavior of ions. Next are several chapters on the behavior of stereoisomeric natural products, including terpenes and terpenoids (Enzell, Dahlmann, Bielawski),
steroids (Tabet), quinolizidine and indole
alkaloids (Tamas) and rotenoids (Kostova, Mollowa). The comprehensive article on the steroids also contains a substantial section on MS-MS “linkedscan” techniques. Other articles report on
organometallic compounds (Nekrasov,
Zagorewskii) , measurements on labeled
compounds (TureEek), and the estimation
of enthalpies of formation (Splitter).
The material contained in the book is
very Comprehensive and well presented,
although the style varies from one author
to another. Often, however, the writers
fail to distinguish clearly between textbook-style presentation and the mere cataloguing of fdcts. For example, the same
basic phenomena are described several
times over, especially in the early chapters. Few theoretical arguments are put
forward to explain the different behavior
of stereoisomers, and the structure of the
book could have been tightened considerably by consistently separating the discussion of basic principles from the chapters
that are more concerned with compound
classes, with appropriate cross-references.
The lack of sufficient coordination between the chapters is also evident in the
dearth of cross-references and the fact
that citations of key publications are often
repeated.
From the user’s point of view one
would have preferred the chapter on
mass-spectrometric methods to devote
more attention to special measurement
techniques and their relevance to distinguishing between stereoisomers. Here a
critical evaluation of the procedures for
determining relative peak heights and the
reproducibility of such data with different
types of instruments would have been
very useful, as also would a discussion of
the methods used for distinguishing between stereoisomers. The application of
MS-MS techniques using the tandem
mass spectrometers that are now becoming more widely available is only touched
on briefly.
The book is well produced with a clear
typeface, a considerable advantage in a
book of this size. It is unfortunate, however, that the publishers have not redrawn
the structural formulas, or at least insisted
on a uniform style. Their quality varies
greatly; often there are no compound
numbers, and in some cases the relevant
text is far removed from the illustration.
However, these criticisms do not alter
the verdict that the comprehensiveness of
the book and the overall high quality of
presentation will ensure that it becomes a
standard work in this field. It can therefore be recommended to all mass spectroscopists involved in the analysis of organic compounds, and to everyone else who
wishes to learn about the capabilities of
mass spectrometry for analyzing stereoisomeric compounds.
Heinrich Luftmann
Organisch-chemisches Institut
der Universitit Miinster (FRG)
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