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d-Orbital Effects in PN and SiC -Electron Systems.

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monomers in the emulsion polymerization (type A), while
the other contains no hydrophilic groups (type S), a mixture
of the two dispersions often coagulates within a few seconds
after preparation. However, addition of a small percentage
of type A can lead to agglomeration of the particles of an
S-type dispersion. For example, when a polybutyl acrylate
dispersion having an average particle size of 800 8, is mixed
with 1 wt-% of a dispersion of a copolymer of 95 % of ethyl
acrylate and 5 % of acrylic acid, followed by adjustment of
the pH to 8-9, a latex having Dn = 6300 8, and Dw= 7300 8,
is obtained. The particles continue to grow on further
addition of any S-type dispersion.
Schemes for the agglomeration were developed on the basis
of particle size distribution functions and with the aid of
latices labeled with polymerizable dyes, as well as by the use
of electron micrographs with special preparation techniques.
The emulsifier sheath is thought to afford the latex particles
only limited protection against association (coagulation).
When latex particles of type S meet only other particles of
the same type, the electrical double layer formed by the emulsifier provides adequate protection against coagulation.
When t y p e 3 particles collide with type-A particles, on the
other hand, irreversible association takes place. Any S
particle coming into contact with the surface of an A particle
is held fast and fused with other particles to form a secondary particle, with the hydrophilic A particle “floating”
o n its surface. The A particle remains active practically
indefinitely, and takes up further S-type particles that may
be added.
[*I Dr. H.-G. Keppler, Dr. H. Wesslau, and Dr. J. Stabenow
Badische Anilin- und Soda-Fabrik AG
67 Ludwigshafen/Rhein (Germany)
New Gels from Cellulose and their Uses in
Chromatography
By H. Determann and Th. Wielandc*]
Spherical cellulose particles are prepared by emulsification of
aqueous solutions of cellulose (in tetramminecopper(I1)
hydroxide or solutions of complex Cd2+ or Fez+ salts) or of
sodium cellulose xanthate in benzene followed by regeneration with organic acids. The density of the network can be
varied by variation of the cellulose concentration in the
complex salt solutions. The beads obtained are substantially
amorphous, whereas those formed on slower precipitation
from xanthate solution contain large crystalline regions. The
efficiency of the new cellulose gels in chromatographic
separations could be seen in the perfect separation of E. coli
bacteria, dextran blue, and benzyl alcohol. The elution
position of the polydisperse high molecular weight dextran
dye depends on the crosslink density.
The new gels can also be used for the separation of macromolecular substances up to the range of microscopically
[VB 118 IEI
visible particles (mitochondria, microsomes).
German version: Angew. Chem. 80. 407 (1968)
[ * ] Dr. H. Determann and Prof. Dr. Th. Wieland
Institut fur Organische Chemie der Universitat
6 FrankfurtIM., Robert-Mayer-Str. 719 (Germany)
Ternary Compounds as Semiconductors
By H.- U. Schuster 1*I
Not only binary compounds with the crystal structure of
zinc blende and of wurtzite but also a large number of
ternary compounds with tetrahedral structures (e.g., chalcopyrite type) are now known to be semiconductors.
400
Semiconductor properties are, however, not confined to
compounds with tetrahedral structures. The semiconductors
MgpSi, MgzGe, and MgzSn crystallize in the antifluorite-type
lattice. In these compounds only the Mg atoms are in tetrahedral environments, and the Si, Ge, and Sn have coordination number 8. Finally a filled antifluorite-type lattice can be
ascribed to the semiconductor Li3Bi [I], the cubic facecentered bismuth lattice having Li atoms occupying not only
the tetrahedral vacancies but also the octahedral vacancies
that are still free in MgpSi. Ternary compounds with a
modified Li3Bi structure are the Li2MgSn prepared by
Laves 121, which according to Mooser and Pearson
has
semiconductor properties, and a series of compounds
prepared during the present investigations:
LiCuzSi
pale violet
LiCuzGe
pale violet
LiAgzSn
pale blue
LizCuGe
medium brown
LilCuSn
dark violet
LizAgSn
deep violet
L i 2 A uSn
orange
These compounds are sensitive to hydrolysis, are prepared
by reaction of the elements in tantalum crucibles under argon,
have a metallic sheen, and, when they contain elements of the
copper group, are colored. Their structure is composed of a
cubic face-centered unit cell of atoms X (X = Si, Ge, or Sn),
whose octahedral vacancies are all occupied by Li and whose
tetrahedral vacancies of the composition LiMZX are occupied
only by IB atoms, and of the composition LipMX are
occupied statistically by IB or I1 B atoms (M) and Li.
On measurement of the electrical resistance in relation to
temperature for polycrystalline samples, the weakly diamagnetic compounds of IB elements show metallic behavior
and compounds of the I1 B elements show semiconductor
properties. Excitation energies were calculated from the
absorption spectra of the germanides of the zinc group
(maxima between 1080 and 1300 nm): A E = 1.10 (LizZnGe),
0.99 (LizCdGe), 0.93 (LizHgGe) eV.
Lecture at Kiel (Germany) on October 26, 1967
[VB 1 1 1 IEI
German version: Angew. Chem. 80, 369 (1968)
[*I Priv.-Doz. Dr. H.-U. Schuster
Institut fur anorganische Chemie der Universitat
23 Kid, Olshausenstr. (Germany)
[l] E. Mooser and W . B. Pearson, J. chem. Physics 26, 893 (1957).
[21 F. Laves, personal communication referred to in [I].
d-Orbital Effects in PN and S i c
jr-Electron Systems
By H. Bock 1*I
Phosphorus-azo compounds X20P-N=N-POX2 are violet;
the n + x* excitation energy of the four-center chromophore P-N=N-P
is unexpectedly low. Investigations by
electron spectroscopy as well as MO calculations o n numerous carbon-azo compounds have led to the assumption that
the long wavelength shift in the absorption maximum is, in
the main, caused by additional d-x* interaction between unoccupied phosphorus 3d orbitals and the N = N x* state“].
To obtain information o n d-orbital effects of this type,
by means of which many differences in properties between
compounds of elements with principal quantum numbers
n = 2 and those with n > 3 are explained under the general
heading of “p,d,-contributions”,
we have used R3Si- and
R3C-substituted compounds as simple models. More than
two hundred derivatives of linear and cyclic, alternant and
Angew. Chem. internat. Edit. I VoI. 7 (1968) I No. 5
nonalternant, isoconjugated and heteroatomic x-electron
systems (polyenes, polyines, aromatic compounds, aryl ethers,
ketones, ketimines) have been synthesized and the relative
energy differences between them have been measured [21:
ground-statechanges by means of vertical ionization potentials
as well as charge-transfer transitions in suitable donoracceptor complexes, and variations in antibonding orbitals
by means of half-wave reduction potentials as well as ESR
coupling constants of radical anions. The total differences
are obtained from the electronic spectra.
The experimental results can be interpreted by different
inductive polarization + ISiR, > + I C R ~ and an additional
electron back-donation Si(d) + C,, which also explain
other characteristic properties of the molecules, such as
stretching and deformation vibrational frequencies,lH-N MR
signals, and dipole moments. Calculations by H M O and
PPP procedures permit correlation and numerical reproduction of the experimental values. Whether the acceptor
function of the R3Si groups simulated in the Si parameters
used are to be ascribed solely to silicon 3d-orbitals and what
degree of importance attaches to the a-states that have so
far been neglected, will be subject of further investigations
on this central problem of inorganic nonmetal chemistry.
Lecture at Braunschweig (Germany) on January 29, 1968 [VB 138 IE]
German version: Angew. Chem. 80, 368 (1968)
[*I Priv.-Doz. Dr. H. Bock
Institut fur Anorganische Chemie der Universitlt
8 Munchen 2, Meiserstr. 1 (Germany)
[l] H . Bock, G . Rudor, E. Baltin, and J. Kroner, Angew. Chem.
77, 469 (1965); Angew. Chem. internat. Edit. 4, 457 (1965).
[2] Cf. preliminary communications: H . Bock e f al., Angew.
Chem. 79, 932, 933, 934, 1106; Angew. Chem. internat. Edit. 6,
941, 941, 943, 1085 (1967); Chem. Commun. 1967, 1299.
Optical Excitation and Ionization of Adsorbed
Molecules
By H. Moesta [*I
The lack of spectroscopic information is felt in our still
unsatisfactory ideas about the nature of the bonding in
adsorption. New methods have now been developed for
UV-spectroscopic investigation of chemisorptive bonding.
Technical requirements are the use of ultrahigh vacuum
processes (UHV) and of an extremely powerful light source
that operates also in the short-wave ultraviolet region
(-800 A) under UHV conditions. Further, methods of
detecting changes in the bonding state are needed that permit
measurement with very small samples (some 1010 molecules).
We have studied:
1. Adsorbed alkali atoms on W and Pt as models for the
investigation of the principal processes.
2. Polyatomic gases such as CO, Nz, H2. NH3, HCN, etc., on
metals such as Fe, Pt, and Ni.
3. NaCl molecules on NaCl cleavage planes as model for
non-metallic systems.
Experiments in project (1) were carried out with a UHV
mass spectrometer and a surface-ionization ion source.
Differences in ionization were observed on irradiation with
visible or near-ultraviolet radiation; this dependence o n
wave length can be correlated with adsorption in shifted or
broadened atomic terms of the adsorbate.
Experiments for project (2) have only just begun. An exploding-wire light source has been developed that delivers
monochromatic light with 1016 quanta per flash behind a
monochromator at 1500 A. Changes in the contact potential
were measured for detecting photoreactions of adsorbed
molecules.
Experiments for project (3) concern the rate of evaporation
of NaCl crystals, which was measured in a UHV microbalance,
Angew. Chem. internat. Edit. J Vol. 7 (196%) / No. 5
(i) with illumination and (ii) without illumination.The evaporation corresponds to desorption of NaCl molecules. The
enthalpy of evaporation decreases on irradiation by light in
the region of the ground lattice absorption.
Findings in the three lines of research were discussed in
relation to catalysis and to modern problems of extraterrestrial chemistry.
[VB 137 IE]
Lecture at Koln (Germany) on January 26, 1968
German version: Angew. Chem. 80, 368 (1968)
[*] Doz. Dr. H. Moesta
Institut fur Physikalische Chemie der Universitat
5 3 Bonn, Wegelerstr. 12 (Germany)
Properties of the AUosteric Forms of Yeast
Glyceraldehyde-3-phosphate-dehydrogenase
By K. KirschnerC*J
At p H 8.5 and 40 “ C nicotinamide-adenine dinucleotide
(NAD) is bound to glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) from bakers’ yeast by a cooperative
process; the saturation curve of the tetrameric enzyme has a
sigmoid shape. Temperature-jump relaxation measurements
have shown that this behavior can be described by Monod’s
allosteric mechanism 111. The isomerization of one allosteric
form of the enzyme into the other is so slow (ti/, = 0.1-5 sec)
that various properties of the less affine T form can be
studied with the aid of the “stopped-flow’’ method. After
rapid mixing of apo-GAPDH with NAD the kinetics of the
formation of the enzyme-coenzyme complex can be followed
by its absorption spectrum. The time course is clearly
biphasic. The first, very rapid phase can be interpreted as
the binding of coenzyme to the preferred form of the preequilibrium (4 N A D + TO + T4). In the second, slow phase
the transient species T4 changes into the stable form R4.
The number of binding sites (n’ = 4) and the dissociation
constant K’ of the T form can both be determined by rapid
titration with NAD; the results agree satisfactorily with those
obtained from relaxation measurements. Further, the difference spectrum of the two formsT4 and R4 was measured by the
same procedure: T4 has a weaker absorption band at 360 nm.
The spectrophotometric titration curve was calculated by
means of the extinction coefficients of T4 and R4 obtained in
this way; agreement with experiment was good.
Similar experiments show that, even when all the substrates
are bound (3-phosphoglyceraldehyde. NAD, and arsenate),
the T form is enzymatically inactive. The kinetic results are
supported by the results of rapid spectrophotometric titration
of the SH groups of the enzyme with Ellman’s reagent [5,5’dithiobis(nitrobenzoic acid), DTNB] in the presence and then
i n the absence of NAD. The two allosteric forms T and R
behave differently: the four identical SH groups of the
enzymatically inactive T form react with DTNB eighty times
faster than those of the R form. To a first approximation the
rate constants do not depend on the presence or absence of
NAD. Quantitative evaluation of the SH titration permits a n
independent determination of the characteristic equilibrium
constants LO and L4 and calculation of the theoretical R
function [21; agreement between experiment and theory is
satisfactory.
[VB 140 IE]
Lecture at Gottingen (Germany) on December 14, 1967
German version: Angew. Chem. 80, 369 (1968)
[*I Dr. K. Kirschner
Max-Planck-Institut fur Physikalische Chemie
34 Gottingen, Bunsenstr. 10 (Germany)
[l] K . Kirschner, M . Eigen, R . Bittman, and B. Voigr, Proc. nat.
Acad. Sci. U.S.A. 56, 1661 (1966).
[2] J. Monod, J. Wyman, and J.-P. Changeux, S. molecular Biol.
12, 88 (1965).
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