вход по аккаунту


Book Review Photochemistry in Organized and Constrained Media. Edited by V. Ramamurthy

код для вставкиСкачать
The last criticism concerns a rather fundamental point.
None of the examples of applications involves systems of
more than one or two dimensions, except for a few rare
literature references to systems of higher dimensionality. It
might be argued that this is justified from a didactic standpoint, insofar as one starts with the simpler cases. On the
other hand, students faced with the arduous task of ploughing through some of the more demanding parts of semiclassical theory may well ask themselves whether it is worth the
effort, since the model systems treated in the book can nowadays be handled numerically by quantum-mechanical methods right from the start, with good accuracy and in a clearly
understandable way. Child has undoubtedly succeeded here
in clearly showing how semiclassical theory can explain
many molecular phenomena. On the other hand, he has occasionally succumbed to the temptation to let formulas run
riot, with results that can only be appreciated by readers who
are already thoroughly familiar with the subject.
What is missing, in my view, is a clear and well-founded
statement of the future outlook for semiclassical theory; one
might claim, for example, that it offers the prospect of
providing a satisfactory description of the dynamics and
spectroscopy of complex multidimensional molecular systems that seem likely to remain untreatable by pure quantum-mechanical methods. But is this in fact true?
To summarize, this monograph is a must for departmental
libraries concerned with theoretical chemistry and molecular
physics. There is no other remotely comparable treatment of
this topical field. However, the book should be read with a
critical attitude.
Jorn Manz
Institut fur Physikaiische und Theoretische Chemie
der Freien Universitiit Berlin (FRG)
Photochemistry in Organized and Constrained Media. Edited
by K Rarnamurthy. VCH Publishers, New York/VCH Verlagsgesellschaft, Weinheim, 1991. XVI, 875 pp., hardcover
D M 236.00.--ISBN 049573-775-213-527-27936-9
How are photochemical and photophysical processes affected when one arranges for them to take place not in one
of the usual solvents, but in a medium that restricts the
mobility of the reactive molecules? For example, how is the
selectivity of the [2 + 2]-photocycloaddition of cinnamic acid
altered if, instead of irradiating the molecules in solution,
one irradiates them in the ordered crystalline form, or how
are the proportions of the different products altered when
photolytic a-cleavage occurs within a zeolite? Can one control the selectivity of a photoreaction by first aligning the
reacting molecules in an ordered environment? What types
of media are suitable as matrices for ordering the molecules
in this way? Such questions are not only of interest for potential applications in synthesis; their answers also yield new
information about the mechanisms of photoreactions and
the structures of the media. One of the scientists who has
made important contributions to the progress of research in
this area is V. Ramamurthy. His experience and knowledge
of this subject was summarized several years ago in a comprehensive review article (Tetrahedron 1986,42,5753- 5839).
An updated and greatly augmented treatment has now been
published in book form. Ramamurthy has brought together
as authors 29 well-known specialists from the disciplines of
organic chemistry, physical chemistry, and biochemistry.
The resulting work can be read either in its entirety, as a
definitive account of organic chemistry in “non-classical”
reaction media, o r selectively to learn about one o r more of
4 ; VCH VerlagsgeseN.scliafi m h H . W-6940 Weinhcim.1993
the specific topics covered in the 19 chapters. Although it is
intended mainly for photochemists, it can also be recommended to other chemists who are interested in finding new
ways of obtaining enhanced selectivity.
In Chapter 1, M. Garcia-Garibay and N. J. Turro explain
their ideas for describing organized, supramolecular systems
in terms of topological geometry. Taking as an example the
r-cleavage of dibenzylketones, they show how different reaction media can be classified and compared from a topological standpoint. The reader thus obtains an insight into the
concepts that underlie the studies described in the later chapters, and also an aid to interpreting the data that are presented.
Chapters 2, 3. 12, and 13 describe modern spectroscopic
methods for studying ordered systems. K. Kalydnasunderam
describes all the most important molecules that can be incorporated into micelles, vesicles, or biological membranes, o r
into cyclodextrins or zeolites, to act as fluorescence probes.
He explains how such probes can be incorporated, and classifies them according to their interactions with the surrounding medium. C. Bohne, R. W. Redmond, and J. C. Scaiano
describe experimental arrangements for laser spectroscopic
studies, and show how these methods can be used to determine the physical properties of microheterogeneous systems;
the main emphasis is on determining physical and kinetic
parameters for micelles. D. Avnir and M. Ottolenghi discuss
photophysical processes involving molecules adsorbed on
the surfaces of heterogeneous catalysts. They start from the
assumption that these surfaces are fractal in nature, and
show that the effects of the surface properties on the reactivity of adsorbed substances can be calculated using exponential relationships of the kind that occur in fractal geometry.
To conclude this group, W. R. Ware shows the kinds of information that time-resolved spectroscopy can yield regarding
the kinetics of fluorescence quenching in microheterogeneous systems. Here again the main emphasis is on micelles,
but work on cyclodextrins, silica gel, and biological systems
is also featured.
The treatment of true photochemistry starts with Chapter 4. Chapters 4-6, consisting altogether of about 170 pages,
deal with photoreactions in crystals, subdivided into biomolecular photoreactions (Ch. 4, K. Venkatesan, V. Ramamurthy), monomolecular photoreactions (Ch. 5, J. R. Scheffer, P. R. Pokkuluri), and the preparation of chiral products
in crystals (Ch. 6, M. Vaida, R. Popovitz-Biro, L. Leiserovitz,
M. Lahav). The last-mentioned chapter contains a particularly interesting account of experiments aimed at using crystal symmetry to produce chiral products from achiral educts.
Unfortunately, however, the quality of reproduction of some
of the figures is poor.
Chapter 7 (V. Ramamurthy) is concerned with photoprocesses involving host-guest complexes in the solid phase. The
center-point of this chapter is Ramamurthy’s own work on
Norrish reactions and photochemically-induced Fries rearrangements in cyclodextrins, but all the other important systems are also given an appropriate amount of space. It is
regrettable that some of the guest systems described as being
suitable for photoreactions are not accompanied by examples of reactions for which they have been used, and also
that some of the figures are of poor quality: even readers
already familiar with the subject will be unable to recognize
in Figure 18 the effect referred to in the text.
Chapters 8-1 1 could be summarized under the general
heading “Photoprocesses of Molecules Adsorbed on the
Surface and in the Interior of Metal Oxides”. In Chapter 8,
L. J. Johnston has collected together the reactions of molecules adsorbed on silica gel and alumina, and arranged them
according to reaction types. W. Jones then describes in Chap-
OS7U-OS33/93j0303-0446$ IO.O/)+ 2 5 . 0
Angew. Cliem Iru. E d EnRl. 1993, 32. No. 3
ter 9 photophysical processes involving molecules intercalated between the layers of clays, micas, and other metal oxide
phases with layer structures. Chapter 10 (V. Ramamurthy)
contains a review of photochemical reactions within zeolites,
which is especially worth reading. Like Chapter 8. Chapter 11, by H. Al-Ekabi, dealing with photoelectron transfer
induced reactions on the surface of semiconductor catalysts.
is again classified according to reaction types.
Photophysical and photochemical processes in liquid crystals form the subject of Chapter 14 (R. G. Weiss). The author
begins by considering photophysical processes in mesophases.
and shows how the analysis of spectroscopic data yields information on the structures of excimers and exciplexes in
these phases. This is followed by detailed descriptions of
various chemical reactions. in particular of Norrish Type I1
reactions and [3+ 21-cycloadditions.
Chapter 15. in which S. P. Spooner and D. G . Whitten
deal with photoreactions in Langmuir-Blodgett films, is again
logically divided into a physical part and a chemical part.
The authors explain how the structure of the film determines
which types of energy and electron transfer mechanisms are
effective, and they describe some of the most important types
of photochemical reactions for chromophores that are incorporated as subunits into the amphiphiles used to form the
films. Examples of such reactions are the cis-trans isomerization of azobenzene. (reversible) [2 + 21-cycloadditions, and reactions of merocyanine dyes. However. the authors d o not
give details of possible applications of Langmuir-Blodgett
films, such as in information storage or in biochemical analysis.
In Chapter 16, A. Ueno and T. Osa describe two particularly interesting types of host-guest complexes, namely cyclodextrin complexes and systems containing crown ether
structures. The section on the photochemistry of cyclodextrin complexes in solution is complementary to the discussion in Chapter 7, where the corresponding solid-phase reactions were described. That on crown ether systems contains
a review of metal cornpiexes that are of potential interest in
relation to the development of an ion-specific photometric
analysis method and the photoinduced transport of ions
through membranes.
Chapters 17 and 18 discuss examples of photochemical
processes in biological systems. C. V. Kumar reports some
findings on details of the photochemistry of photosynthesis,
and describes the use of DNA as an organized medium for
influencing the selectivity of photochemical processes.
R. S. H . Liu and Y Shichida show how the cis-trans isomerization of retinal in rhodopsin is influenced by the protein
environment. The collection ends with an article by D. F.
Eaton (Chapter 19), giving some interesting examples of potential technological applications of photochemistry in organized media.
It is unfortunate that this otherwise very comprehensive
and detailed collection of articles on photochemistry in organized systems includes nothing on the particularly important
topic of micelles. The explanation given in the preface is that
to include this would have exceeded the planned size of the
book, and also some up-to-date reviews are already available. This is not very convincing, since every chapter in the
book begins by referring to other relevant review articles,
some of which are very recent. Indeed, the particular advantage of this book is that it gathers together information frotn
a wide range of specialist areas and journals, so that one can
recognize parallels leading to ideas for new experiments.
However, despite this gap in coverage, the principle of
having an expert to report on each specialist topic means that
the reader gets a wealth of up-to-date information at first
hand. Ramamurthy has succeeded remarkably well in
matching together the individual contributions and avoiding
repetition. Frequent cross-references to related areas of
work in other chapters are included. The incidence of printing errors is remarkably small. and there are no really serious
errors that could lead to misunderstandings. This demonstrates the wisdom of Ramamurthy's practice of having each
article cross-checked by three expert referees, and the work
as a whole checked again by P. de Mayo and N . J. Turro.
Finally, Ramamurthy has collected all the manuscripts together and used the computer to put them into a uniform
format. Only someone who has previously undertaken such
a task will appreciate how much time and patience it requires. The version finally seen by the reader is a photographically reduced and bound copy of the computer printout. Nevertheless, it must be said that, although the printout
appears superficially very neat with a close resemblance to a
normal printed text, it is appreciably less agreeable to read
than, for example. a typewritten transcript of a lecture. The
characters produced by the laser or ink-jet printer are simply
too thick and lacking in sharpness when reproduced in the
size that is appropriate for a book page. It would have been
better, and perhaps more economical, if the text could have
been typeset directly from the computer.
Thomas Rumhucli
Organisch-Chemisches Institut
der Universitiit Miinster (FRG)
State Selected and State-to-State Ton-Molecule Reaction Dynamics. Part 1: Experiment, Part 2: Theory. (Series: Advances in Chemical Physics, Vol. 82.) Edited by C.- YI Ng
and M . Baer. Wiley, Chichester, 1992. Pt. 1 : XIII, 686 pp.,
hardcover E 109.00, $164.00.-ISBN 0-472-53258-4; Pt. 2:
XIII, 561 pp., hardcover E 109.00, $ 164.00.-ISBN 0471-53263-0
The time is ripe for the publication of a textbook on the
subject described by the above title, and in these two volumes
the editors have achieved an important step in that direction.
It is a collection of soundly prepared review articles, eight in
each volume, on experimental investigations into ionmolecule reactions (Pt. 1) and their theoretical treatment
(Pt. 2), which presents the current state of research in this
field, and also discusses promising new methods of investigation. Research into the reaction dynamics of ions is important not only in relation to processes occurring in interstellar
space, the atmosphere, and plasmas, but also for contributing to a better fundamental understanding of reactions between neutral species.
The dynamics of ion-molecule reactions is, of course, predominantly influenced by long-range ion-multipole interactions, and probably the most important difference compared
with reactions between neutral reactants is in the mechanisms of charge transfer. Nevertheless, many of the experimental and theoretical methods used are similar in the two
cases. For example, resonance enhanced multiphoton ionization (REMPI) provides a bridge between studies of neutral-neutral and of ion-molecule reactions, serving in the
former case as a state-selective detection method, and in the
latter as a means of state selection for the ionic reactants.
The absolute reaction cross-section for an ion-molecule
reaction can be determined relatively easily up to very high
collision energies. However, it is more difficult to investigate
collisions with low energies in the meV range. The problems
can be partly overcome by using well-defined ion beams in
conjunction with inhomogeneous radiofrequency ( R F ) fields
Без категории
Размер файла
308 Кб
photochemistry, ramamurthy, book, organized, constraint, edited, media, review
Пожаловаться на содержимое документа