Optically Active Polymers

420 Pages·1979·17.137 MB·English

by  Ignacio Tinoco Jr. (auth.), Eric Selegny (eds.)

CHARGED AND REACTIVE POLYMERS
VOLUME 5
OPTICALLY ACTIVE POLYMERS
CHARGED AND REACTIVE POLYMERS
A SERIES EDITED BY ERIC SELEGNY
VoL 1: POLYELECTROLYTES. Papers initiated by a NATO Advanced Study Institute
on 'Charged and Reactive Polymers', held in France, June 1972.
Edited by Eric Selegny and co-edited by Michel Mandel and Ulrich P. Strauss
2: POL YELECTROL YTES AND THEIR APPLICATIONS
Edited by Alan Rembaum and Eric Selegny
3: CHARGED GELS AND MEMBRANES - Part I
Edited by Eric Selegny and co-edited by George Boyd and Harry P. Gregor
4: CHARGED GELS AND MEMBRANES - Part II
Edited by Eric Selegny
VOLUME 5
OPTICALLY ACTIVE
POLYMERS
Edited by
ERIC SELEGNY
Universite de Rauen, France
D. REIDEL PUBLISHING COMPANY
DORDRECHT : HOLLAND / BOSTON: U.S.A.
LONDON:ENGLAND
UbraIY of Congress Cataloging in Publication Data
Main entry under title:
Optically active polymers.
(Charged and reactive polymers: v. 5)
Includes bibliographical references and index.
L Polymers and polymerization -Optical properties. 2. Optical rotation.
3. Circular dichroism. l. Sclcgny, Eric. II. Series.
QD38L8.067 547' .84 79-16124
ISBN-13: 978-94-009-9380-8 e-ISBN-13: 978-94-009-9378-5
001: 10.1007/978-94-009-9378-5
Published by D. Reidel Publishing Company,
P.O. Box 17, Dordrecht, Holland
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by D. Reidel Publishing Company, Inc.
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All Rights Reserved
Copyright © 1979 by D. Reidel Publishing Company, Dordrecht, Holland
Softcover reprint of the hardcover I st edition 1979
No PaIt of the material protected by this copyright notice may be reproduced or
utilized in any form or by any means, electronic or mechanical,
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retrieval system, without written permission from the copyright owner
TABLE OF CONTENTS
INTRODUCTION vii
IGNACIO TINOCO, JR. / Circular Dichroism of Polymers: Theory and Practice
ERIC SELEGNY and LILIANE MERLE-AUBRY / General Methods of Synthesis
of Optically Active Polymers 15
FRANCESCO CIARDELLI, EMO CHIELLlNI, and CARLO CARLINI/Synthesis
of Optically Active Polymers from Unsaturated Monomers 83
NICOLAS SPASKY, PHILIPPE DUMAS, and MAURICE SEPULCHRE / Synthesis
of Optically Active Polymers from Cyclic Monomers by Stereoelective Polymeri-
zation 111
DRAGUTIN FLES / Optically Active Poly-Propiothiolactones 143
YUH MINOURA / Asymmetric Synthesis in Radical Polymerization 159
LIA ADDADI, MENDEL D. COHEN, and MEIR LAHA V / Synthesis of Chiral
Non-Racemic Dimers and Polymers Via Topochemical Reactions in Chiral
Crystals; an Example of an 'Absolute' Asymmetric Synthesis 183
GIORGIO MONTAUDO and PAOLO FINOCCHIARO / Conformational Properties
of Stereoregular Polyamides with Varying Degrees of Structural Rigidity 199
J.G. HAMIL TON, K.J. IVIN, L.C. KUAN-ESSIG, and P. WATT / Some Properties
of Optically Active Poly (N-Formylpropylenimine) 219
PIERO SALVADORI / Circular Dichroism and Conformation in Copolymers with
Aromatic Side Chains and in Low Molecular Weight Models 225
E. PEGGION, A. COSANI, M. TERBOJEVICH, and M. PALUMBO / Conformatio
nal Studies on Synthetic Polypeptides, Contribution to the Optical Activity
from Side-Chain Chromophores 231
M. RINAUDO and A. DOMARD / Circular Dichrosm on o-L-Glutamic Acid Oli-
gomers 253
Z .A. SCHELL Y / Conformational Dynamics of Optically Active Linear Biopoly-
mers 259
ROLF C. SCHULZ / Modification of Chiral Properties Due to Interaction of
Polymers and Small Molecules or Ions 267
MICHEL VERT I Optical Activity of Reactive 'Non-Regular' Synthetic Polymers.
Properties and Applications 291
JUN JI FUR UKA WA I Inversion of Optical Rotation of Poly(propylene Oxide)
by Solvent 317
G. SMETS and c. SAMYN / Synthesis, Ring Opening Study and Properties of
Some New Po1yampholytes from Substituted Aziridines 331
MANLIO PALUMBO, ALESSANDRO COSANI, MARIA TERBOJEVICH, and
EV ARISTO PEGG ION I Solution Properties of IronIII Complexes of Acetoace
tylated Poly-L-Lysine, Poly-L-Omithine and Poly-L-Diaminobutyric Acid 345
vi T ABLE OF CONTENTS
DANIEL GLAUBIGER / Studies on Complexes of Antineoplastic Agents with
DNA 351
PIER LUIGI LUISI/Synthetic Optically Active Polymers as Catalysts for Asym-
metric Synthesis 357
GEORG MANECKE and WOLFGANG LAMER / Separation of Enantiomers with
Insoluble Optically Active Polymers 403
INDEX OF SUBJECTS 411
INTRODUCTION
The first four volumes of the series on 'Charged and Reactive Polymers' have been
devoted to polymers in solution (Voh. I and II) or in gel and membrane forms (Vols. III
and IV). In correlation with charges, other physical or chemical properties of macro
molecules have been considered. Understanding of charge and hydrophobic effects is
equally important for synthetic and biopolymers or their systems.
Optically Active Polymers are related to problems of the same class, since optical
activity is an inherent property of both natural macromolecules as well as a great variety
of polymers synthesized in the Jast twenty years.
Optical activity is a physical spectral property of chiral matter caused by asymmetrical
configurations, conformations and structures which have no plane and no center of
symmetry and consequently have two mirror image enantiomeric forms of inverse optical
rotation. The racemic mixture of chiral enantiomers is optically inactive.
The most common form of optical activity was first measured at a constant wavelength
by the angle of rotation of linearly polarized light. More recently the measurements
have been extended to the entire range of visible and attainable ultraviolet regions where
electronic transitions are observed, giving rise to the ORD technique (Optical Rotatory
Dispersion). The Cotton effects appear in the region of optically active absorption bands;
outside of these bands the plain curve spectrum is also dependent on all the electronic
transitions of the chromophores.
Circular Dichroism (CD) is observed in the region of active transitions; this technique
has arrived at the level of standard measurements even more recently than ORD.
The relation between chirality, absolute S and R configurations, chromophores and
optical activity is the source of theoretical and experimental questions that are answered
very fruitfully by examining many different compounds. I think that it was Dr Velluz,
one of the pioneers in experimental CD, who advised us to 'fIll up a cupboard with
optically active compounds' as a first act of any research on optical activity. - To fIll;
but how? and why?
The theoretical and experimental work of leBel, Van 't Hoff and Pasteur long ago
demonstrated the relation between optical activity and the 'asymmetrical carbon atom '.
Such an atom, with its four different substituents has a chiral configuration. In a mole
cule, it is a chiral center, and this communicates to the molecule the possibilities of
asymmetrical behavior and rotatory power. Tetravalent heteroatoms such as N, P and S
can be chiral and can cause optical activity.
The great majority of natural molecules contain chiral centers and are optically active.
This is the case because living systems and their extracts as enzymes are able to produce
completely stereoselective asymmetrical synthesis or transformations. This led Pasteur
to say that 'life is asymmetrical' - at the molecular level. The majority of food and
drug molecules of physiological activity are chiral.
Means and ways of asymmetrical synthesis from prochiral species, as well as trans
formations of chiral species, are constant aims and occupations of organic stereochem
vii
viii INTRODUCTION
istry. The preparation of chiral drugs, for example, is a practical consequence of progress,
but the general effort to imitate or equal nature issues from a fundamental conceptual
vein. One should remember (1) that the 'vital force' theory receded as a consequence of
total and asymmetrical syntheses.
A good part of our knowledge of chemical reactions and their mechanisms was gained
through chiral compounds. It is particularly valuable in this respect to be able to follow,
through optical activity measurements the appearance, disappearance, or inversion of
chiral configurations.
Non-asymmetrical syntheses result in optically inactive racemic mixtures of the
enantiomers. They can be separated by one of the three basic Pasteur methods (or their
more recent variants) where, using asymmetrical chemical or biochemical agents, one of
the optical isomers is stereoelectively extracted or transformed. The much greater differ
ence between the diastereoisomers obtained containing non-inverse chiral centers (as
between the two enantiomers) seems absolutely fundamental in all these methods and
techniques based on specific interactions and reactions. The prinCiple that asymmetry is
generated or selected by asymmetry has not yet been contradicted.
Atropic molecules without any materialized asynunetrical center (carbon ur hetereo
atom), can have a chiral conformation and optical activity. Limitations of free rotation
around bonds by intramolecular links or steric hindrances engage such molecules into a
helical conformation, and their 'mirror plane' passes through bonds and not through
atoms. Organic chemistry gave the first synthetic examples of such molecules.
In Forges, Professor Blout has recalled that the chirality of helical conformation
did not escape the attention of Pasteur himself. To go beyond the first steps of a helix
long chains are needed; they were then unknown and Pasteur exemplified his idea by
the image of a spiral staircase. This was long before the discovery of the macromolecular
polypeptide a-helix based on X-ray studies by Pauling and Bragg, and the identification
of the DNA double helix by Watson and Crick. The systematic investigations on optical
activity, ORD and CD related to these ordered conformations in biopolymer solutions
have followed.
Configurational and conformational chiralities cannot only coexist but they also
can induce each other. The left- or right-handed chiral carbon in a chain preferentially
leads to inverse helixes. This was established with natural or denatured biopolymers
or their simplified analogues. For the calculation of the 'helix content' from ORD
measurements, the semi-empirical Moffat equation proves valuable when the existence
of the helix is itself well established.
There is much less evidence to demonstrate the existence of a helix starting from
optical measurements, since configurations other than helically ordered ones, such as
(3-turns or solvent and environmental effects, associations and ionisations, also modify
the electronic transitions.
New theoretical approaches, new models, new chromophores, combinations of tech
niques and even new methods have become necessary.
Synthetic Optically Active Polymers (OA) had scarcely been explored before 1955.
Now two decades later, due to a sudden intensive world-wide contribution, nearly all
the shelves of a huge 'virtual cupboard' are fIlled up with samples. - Stereospecific,
stereoelective and stereoselective initiators or catalysts have been found and cocatalysts
experimented with. Most classes of polyaddition or polycondensation polymers, soluble
INTRODUCTION ix
or crosslinked now count optically active members among their members. Consequently
much has been learned.
With stereospecific heterogeneous phase Ziegler-Natta initiators the prochiral vinyl
monomers are regularly enchained head-to-tail, each double bond is preferentially opened,
and all the tertiary carbons of the obtained isotactic chain have the same configuration.
In spite of this stereocontrol, the homopolymers are optically inactive (except the end
groups) because of intrachain symmetries resulting from the internal compensation in
their diads, of the created chiral units. The compensation is even more evident with
syndiotac tic polymers in which tertiary carbon atoms of inverse configuration alternate
in the chain. Polymers obtained by stereospecific ring opening polymerization show the
same properties.
The inactivation effect by intramolecular compensation observed with low molecular
weight compounds, is much more striking with high polymers, with the end group contri
bution being much smaller as the molecular weight increases.
Chiral centers can and could be generated or introduced in the lateral chains of poly
mers by many available methods. The stereocontrols in the main chain have greater
limitations.
Chirality and optical activity in the main chain need stronger short range asymmetry
at the level of the repetitive unit. The enchainment of some cyclic or diunsaturated
monomers, a few copolymers and mainly the inclusion of symmetry breaking hetero
atoms in the main chain led to such results. This situation makes polycondensations
easier to handle.
Preferential stereoselective incorporation of an enantiomeric monomer or its elective
polymerization from racemic mixtures were accomplished with O.A. chiral catalysts,
and it was also discovered that chiral crystalline structures can transfer asymmetry to a
polymerization mechanism.
Different groups have opened and followed different lines of research: for the first
one, the immediate aim was to add a new type of compound to the list. The second
one was interested in the diversity of the steric environment of one specific chromo·
phore or the flexibility of the chain - in addition to either chain regularity or irregu
larity or, again, the distance of a chiral center from the chain, the size of groups linked
to the chiral center, or their ionizability or reactivity. Some others concentrated on
stereoelective or selective initiators and initiation or propagation mechanisms. In addi
tion, polymerizations with ionic or free radical initiators, homogeneous, heterogeneous,
or on a matrix, as well as step-by-step syntheses and many polycondensations have been
investigated. And in each case the nonracemization during polymer preparation had
to be verified.
From monomers of natural origin as amino acids to purely synthetic atropic monomers
or those with two chiral centers and from polyhydrocarbons to polyelectrolytes, com
plexing polymers and polypeptides the list is long and is further lengthened by the chem
ical transformations of the polymers obtained. During these investigations new monomers
have been synthesized and model molecules, dimers, and oligomers were necessary to
perform physicochemical and spectral studies.
Major questions concerning the differences between small and big molecules and
between natural and synthetic polymers oriented a part of the effort to verify the
existence or nonexistence of ordered polymer conformations and of molecular or ionic
interactions.
x INTRODUCTION
Many optically active polymers have been tested for the selective extraction of chiral
polymers or small molecules from their racemic mixtures or as chiral catalysts.
The theoretical and practical application of these studies in chemistry or physical
chemistry are quite evident. It is also certain that the learning gained by study of syn
thetic polymers can contribute to the refinement of the techniques used to purify and
study biopolymers and the interpretation of measurements through progress made in
biophysical chemistry. But there is still more.
Asymmetry is so strongly associated with living systems that few are the scientists
working on optically active compounds who do not have the feeling of contributing
to the progressive understanding of life's marvelous enigma. This is immediately under
standable when components of biological systems are studied.
The present is analysed by science and future events can sometimes be anticipated.
As for the past, the elimination of impossibilities is often the best that scientific rationalism
can do.
Nevertheless the possible origin of the primary asymmetry linked to the origin oflife
- yesterday a matter of purely philosophical speculation - is nowadays openly appraised
by scientists as more-or-less absolute syntheses of chiral molecules are achieved under
environmental conditions, or in the presence of inorganic or geological materials. Such
experimental conditions are quite restrictive and the yields small.
Even the preferential transfer of asymmetry is not universal in systems containing
asymmetric molecules in the sense that complementary sterical and physicochemical
conditions must be fulfUled to make it effective. Simplified models and synthetic small
and big molecules are very useful in exploring such conditions as the confrontation of
apparently unlucky results with more successful ones, favoring better understanding
of facts and reasons.
There is still much to learn about the reasons for this so extraordinarily perfect but
complex biological stereospecificity; but there is enough evidence for the necessity of
macromolecules.
It is supposed today that if the two mirror-image forms of life could have originally
had similar chances, the propagation of the one that developed good stereospecific
extractive and catalytical systems would quickly have outweighed the inverse fonn.
This has been expressed by my sister Eva by saying, in a humorous way: "It is written
that Kain has killed Abel".
The first International Advanced Study Institute (ASI) on Optically Active Polymers,
(the third ASI on Charged and Reactive Polymers) was held in Forges-les-Eaux, France
in 1975.
Its objectives and topics were announced as follows:
Objective
Investigations on synthetic or natural chiral macromolecules making use of rotatory
power, ORD or CD techniques, to study conformational or interactional problems.
The narrow field of Synthetic Optically Active Polymers has progressively expanded
during the past decade. Evaluations and confrontations of results and interpretations
are now needed with polymers of the purely synthetic world and with those which
nearly imitate nature and are effective model molecules.
Thus, the aim of the Institute is to present critical reviews and illustrative lectures