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Energy Coupling and Electron Transport.

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C O N F E R E N C E REPORTS
with ordinary carbenium ions, such as the tendency to
isomerize[6]or to rearrange by way of ion pairs. Detailed
mechanistic studies are in progress in several laboratories.
Formation and Detection of Vinyl Cations
By C. A . Grab"'
Vinyl cations ( I ) , unknown and rejected a few years ago,
are now the subject of an increasing number of investigations. In these cations the formal positive charge resides on
the carbon atom of an olefinic double bond. With twopresumably linearly-attached ligands they belong to the
group of disubstituted carbenium ions.
(1)
(2)
(a),
R
Lecture at Leverkusen, April 19,1972 [VB 338 IE]
German version: Angew. Chem. 84,592 (1972)
[I] C. A . Grob and G . Cseh, Helv. Chim. Acta 47, 194 (1964).
[2] C. A . Grob and R. Spaar, Tetrahedron Lett. 1969,1439; Helv. Chim.
Acta 53, 2119 (1970).
[3] M . Hunack and T Biissler, J. Amer. Chem. Soc. 91, 2117 (1969);
S. A. Sherrod and R . G. Bergmann, ibid. 91,2115 (1969).
[4] C. A . Grob and H . R . Pfuendler, Helv. Chim. Acta 54,2060 (1971).
[5] C . A . Grob and H . R. Pfaendler, Helv. Chim. Acta 53, 2130 (1970).
[6] C. A . Grob and R. Nussbaumer, Helv. Chim. Acta 54,2528 (1971).
(31 -
= Aryl
(b), R = A l k e n y l
(c),
R
= Cyclopropyl
Energy Coupling and Electron Transport
The objections which have frequently been raised against
the existence of vinyl cations are justifiable inasmuch as
simple vinyl halides (2) (x = halogen) resist hydrolysis
and do not precipitate silver halide from aqueous silver
nitrate as is observed with alkyl halides. However, an
electron donating aryl substituent in the a-position, as in
( 2 4 , can promote ionization under relatively mild conditions, as was first shown in 1964"l. Thus a-halo styrenes
( 2 a ) react in aqueous alcohol to form ketones (via the
enol), enol ethers, and acetylene derivatives by the S,l-E
1
mechanism. u-Alkenyl (2 b )
and a-cyclopropyl substituents (2c) 13) likewise increase reactivity.
The reaction rates of a-aryl substituted vinyl bromides of
the type (2a) depend on substituents in the benzene ring
in a predictable manner. Since they are not influenced by
the hydrogen ion concentration of the medium a mechanism involving acid-catalyzed hydration to the intermediate (3)[41can be excluded.
0
R,C=C-CH=CR;
R &- ~1 - & H = ~ R L
Br
(5)
R,C=C=CH-CR;
By Britton Chance"'
In recent years titrations of redox potentials of the redox
components of respiration chains (flavoproteins, ubiquinones, cytochromes) have led to a new classification of
the components of respiration chains. In this scheme four
groups of redox systems are differentiated, within each of
which the potential is approximately the same and fixed :
1. Flavoproteins and iron-sulfur proteins in the region
- 300 mV ;
2. Flavoproteins, iron-sulfur proteins, ubiquinones and
cytochrome b, in the region 0 mV ;
3. Cytochrome c,, c and a, as well as copper- and ironsulfur proteins in the region 240 mV ; and
+
4. Oxygen in the region
Electrons are moved from one of these groups to another
by means of electron transport components of alternating
redox potential. They adjust their potentials to those of the
acceptor or donor groups in the redox systems of fixed
potential which function as redox buffers; the energy loss is
minimal[''. The transport systems are called energy transducer components. The nature of the transducer components of the first and second groups is unclear, but cytochrome b, was recognized by redox potential titrations
and kinetically as the transducer component between the
second and the third group, and cytochrome a3T spectrophotometrically as the linking compound between the
third group and oxygen.
H3CyJBr
CH3
It is noteworthy that the solvolysis rates of 2-bromodienes
( 4 ) are hardly influenced by the presence of one or two
methyl groups on C - I [ ( 4 ) , R=CH,]. However, two
methyl groups on C-4 [ ( 4 ) ,R'=CH,] accelerate the reaction by more than five powers of ten, as expected on the
basis of the electron distribution in the mesomeric vinyl
cation ( 5 ) . However, charge delocalization can only occur
if C-1, C-2, and C-3 have a linear arrangement, as required
by the limiting allenic form. If this alignment is
prevented, as in the cyclic bromodiene (6), the negligible
solvolytic reactivity characteristic of vinyl halides returnsr5]. Vinyl cations have many features in common
This classification has been supported by analysis of the
kinetic models by computer simulation and by optimization of the kinetic constants for suitable mechanisms. In
particular it was possible to differentiate cytochromes a
and a3Tby measuring the kinetics of the reaction with oxygen at low temperatures (in presence of ethylene glycol
down to -30°C)[21. In these experiments reaction of the
respiratory system of intact mitochondria with oxygen was
initiated by using a laser flash to decompose a preparation
["I
[*I
Prof Dr. C. A. Grob
Institut fur Organische Chemie der Universitat
CH-4056 Basel, St.-Johanns-Ring 19 (Switzerland)
544
+- 840 mV.
Prof, Dr. B. Chance
Johnson Research Foundation,
University of Pennsylvania, Medical School
Philadelphia, Pennsylvania (USA)
Angew. Chem. internut. Edit. 1 Vol. 11 (1972) N o . 6
saturated with carbon monoxide. It proved possible to
measure directly the initial reaction of cytochrome a3 with
-
[I] D. F . IVkon and P. L. Dutton, Biochem. Biophys. Res. Commun.
39,59 (1970);Arch. Biochern. Biophys. 136,583 (1970); B. Chance, D. F .
Wilson, P. L. Durron, and M. Erecinska, Proc. Nat. Acad. Sci. USA 66,
1175 (1970): D. F . Wlsun and P. L. Dutton in T E. King and M . Klingenberg. Electron and Coupled Energy Transfer in Biological Systems.
Dekker, New York 1971, Vol 1, p. 221; D. F . Wlson, P. L. Duttori,
M . Erecinska, J . G . Lindsay, and N . Sato, Accounts Chern. Res., in press:
7: Ohnishi, D. F . CtSlson, 7: Asakura, and B. Chance, Biochem. Biophys.
Res. Commun. 46, 1631 (1972); M . Erecinska, B. Chance, and D. F .
Wlson. FEBS-Lett. 16,284 (1971); M . Erecinska, D. F . Wflson, Y. Mukui,
and B. Chance. Biochem. Biophys. Res. Commun. 41, 386 (1970);
P . L. Dutron. D. f. W s o n , and C. P . Lee, Biochemistry 9, 5077 (1970);
B. Cliance: FEBS-Lett., in press; D. DeVault, Biochim. Biophys. Acta
225, 193 (1971)
[2] E. Chance and M . Erecinska, Fed. Proc. 31,416 (1971), Abstr. 1113;
M. Erecinska and B. Chance, Arch. Biochem. Biophys., in press.
[3] D.F. Wlson, J . G . Lindsay,and J . Brocklehurst, Biochim. Biophys.
Acta, in press.
oxygen by the usual disappearance of absorption at 444 nm
and, further, by hitherto unobserved disappearance of the
absorption at 600 nm together with appearance of a small
but significant absorption band at 428 nmL3];in that work a
new intermediate compound of oxygen and cytochrome
a3, formed extremely rapidly, was identified, whose spectral
properties indicated the presence of an oxygenated cytochrome a3-FeZf compound. Reaction kinetics at room
temperature, redox titrations and computer analysis of the
kinetics indicate that the reaction product of cytochrome
a3and oxygen achieves a potential below that of cytochrome
a prior to electron transfer between the two. By analogy
with the behavior of hemoglobin it is probably to be
expected that drastic changes in the conformation of
hemin will occur on alteration of the redox potential of
the components and of their spectral properties.
[Lecture at Dortmund on February 22, 19721 [VB 337 I€]
German version: Angew. Chem. 84,553 (1972)
R E V I E W ABSTRACTS
Formation of alkali metal complexes in solution is the subject of a review by R. Winkler. General characteristics of
complex formation reactions are outlined in the introduction, and specific properties of alkali metal complexes are
then described. Several techniques are mentioned for
measuring rate and equilibrium constants for complexation reactions of alkali ions with the indicator and model
ligand murexide in methanol. The article closes with a
detailed discussion of the properties of biological substances
with specific alkali ion carrier function, e. g. antibiotics with
cyclopeptide, cyclodepsipeptide, or macrolide structure.
[Kinetics and Mechanism of Alkali Ion Complex Formation in Solution. Structure and Bonding 10, 1-24 (1972);
38 references]
[Rd 503 IE -HI
The bonding properties of inorganic pseudohalides with the
triatomic groups azide, fulminate, cyanate, and thiocyanate
are discussed by Z . Iqhal. Data about molecular and lattice
geometries, vibrational and electronic spectra, lattice
energies, and energies of formation are used for comparisons of these types of compounds. A special chapter is
devoted to the exotic thermal behavior of azides and fulminates. [Intra- and Inter-Molecular Bonding and Structure
of Inorganic Pseudohalides with Triatomic Groupings.
Structure and Bonding 10, 25-55 (1972); 86 references]
[Rd 504 IE -H]
Current views of bonding in carbonylmetal compounds are
treated by P. S. Braterman. The review provides a qualitative description of the metal-carbon bond in terms ofmolecular orbital theory and of bonding in polynuclear compounds without or with direct metal-metal interaction. In
a second (smaller) section theoretical attempts at quantitative evaluation of energy states of carbonyls are discussed.
[Spectra and Bonding in Metal Carbonyls, Part A: Bonding. Structure and Bonding 10, 57-86 (1972); 110 references]
[Rd 505 IE -H]
The theory of the magnetic properties of polynuclear transition metal compounds is reviewed by J. S. G r i f f h . The
Angew. Chem. internat. Edit. i Vol. 11 (1972) i N o . 6
treatment of anisotropic g tensor interaction leads to a
closed expression for the susceptibility of binuclear compounds. For the treatment of three (or more) coupled
magnetic moments the Racah and Wigner irreducible
tensor method is used. Three-body interactions and the
fine structure of degenerate ground states are also considered. As an example, the magnetic properties of proteins with
two sulfur-bridged iron ions (spinach ferredoxin) are discussed. [On the General Theory of Magnetic Susceptibilities of Polynuclear Transition-metal Compounds. Systems
with Two or Three Spins. Structure and Bonding 10,87 to
126 (1972); 93 references]
[Rd 506 IE -HI
The thermochemistry of the chemical bond is discussed by
I/: Gutmann and U . Mayer. Starting from a critical evaluation of Pauling’s concept of bond energy, electronegativity.
and ionicity a new approach is suggested to describe the
ionic character of a bond (valid only for that bond in a
specified molecule) with the aid of thermochemical data.
The new values of ionic character appear in some cases to
be more reasonable than Pauling’s values, but they require
a knowledge of the bond energies of the homoatomic molecules. A concept to circumvent this difficulty in the treatment of metal compounds is outlined. [Thermochemistry
of the Chemical Bond. Structure and Bonding 10,127-151
(1972); 6 references]
[Rd 507 IE -HI
Spectra and structural properties of complex tetracyanides
of platinum, palladium, and nickel are reviewed in two
papers by S. Jerome-Lerutte and M . L. Moreau-Colin. The
former is concerned with the vibrational spectra of this
group of compounds and with the force constants derived
from them ; the latter discusses their electronic spectra. A
distinction is made between the spectra of “free” ions (in
solutions)and the spectra ofcrystalline compounds. Finally,
the luminescence of the tetracyanoplatinates is mentioned.
[Vibrational Spectra and Structural Properties of Complex
Tetracyanides of Platinum, Palladium, and Nickel. Structure and Bonding 10, 153-166 (1972); 35 references.Electronic Spectra and Structural Properties of Complex
545
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