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Crystal Growth from the Vapor Phase.

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C O N F E R E N C E REPORTS
Crystal Growth from the Vapor Phase
By R . Nitsche[*1
Successful solid-state research requires the production of
single crystals of high purity with defined doping and few
structural imperfections. Most crystal growth methods are
based o n the solid-liquid phase transition, i.e. they involve
the use of melts or solutions. These methods cannot be used
for substances whose melting points are difficult to reach
experimentally, that decompose or sublime prior to melting,
or for which n o suitable solvents exist.
To close these gaps, increasing use has recently been made of
vapor-phase methods. Whereas sublimation is confined to a
relatively small number of volatile substances, gas reaction
methods are very widely applicable. In these methods a gaseous mixture yielding the solid phase reacts under controlled
conditions in a growth chamber in the presence of seeds. The
gas mixture is transported to the seed by:
a) Blowing separate gas streams into the growth chamber
(flow transport).
b) Reaction of the polycrystalline feed material from which
crystals are to be grown with a gas at temperature T I to give
one (or several) volatile compound(s), transport of the gas
mixture, whose composition corresponds to the heterogeneous equilibrium at T I , to the seed (at T2) by diffusion, convection, or flow, and reversal of the reaction with deposition
of the solid phase according to the equilibrium conditions a t
Tz (chemical transport).
c) Combination of a and b.
With skilful control (low supersaturation, good temperature
stability), gas reactions can yield crystals of considerable size
having high purity and structural perfection. Crystals of
elements and binary compounds (oxides, sulfides, phosphides,
etc.), as well as of many ternary and quaternary compounds
have been grown.
Two types of apparatus are used:
1) Closed systems (mostly sealed quartz tubes) for automatic
chemical transport in the temperature gradient between the
solution chamber ( T I )and the growth chamber (Tz).
2) Open systems for chemical transport in flowing gases
between TI and Tz or for direct combination of separate gas
streams.
(1) Is particularly suitable for the growth of large crystals over
long periods, and (2) for the growth of monocrystalline layers
on oriented substrates (epitaxy), for which less time is required. Continuous or abrupt modification of the crystal
composition (i.e. formation of solid solutions or doping) is
possible during growth.
[VB 214 IE]
Lecture at Stuttgart on October 16, 1969
German version: Angew. Chem. 82, 48 (1970)
. .
[*I Prof. Dr. R. Nitsche
Kristallographisches Institut der Universitat
78 Freiburg, Hebelstrasse 25 (Germany)
Structure and Function of Cell Receptors
There has been no lack of experiments designed to modify
the mode of action of biologically active substances by
chemical changes. However, such a n approach becomes all
the more difficult t o justify the more complicated the mode
of action of a substance is.It would therefore appear advisable
to limit primary studies o n the reactions between substances
and their cell receptors to in-virro systems that are as simple
and comprehensible as possible, Such systems are currently
being developed.
In this way the action of digitalis glycosides o n cell membrane
components that are designated transport adenosine triphosphatase can be tested “1. Studies in which the action of
receptors on artificial lipid membranes can be measured
appear particularly promising. The effect of transport adenosine triphosphatase and digitalis compounds o n the
permeability of bIack lipid membranes may be cited as a
model [*I.
Considerable interest attaches to the analysis of cell receptors in virology too. It is a known fact that a virus infection can only occur when the infectious agent becomes
bound to a corresponding cell surface. Virus-binding cell
receptors have been isolated and some of them characterized
for a number of different viruses. The best-known receptors
include those for certain phages and for myxoviruses.
The components isolated primarily by Weidel et al. [31 from
cell walls of E. coli are lipoproteins and/or lipopolysaccharides that react specifically with certain T-phages. Cell
receptors for myxoviruses (influenza and parainfluenza
viruses) contain acylated neuraminic acid [4J, whose structure
has been completely elucidated 151, as receptor-dominant
sugar. The component of the myxoviruses which reacts
specifically with the neuraminic acid of the cell, i . e . the
enzyme neuraminidase, has been isolated in highly pure
form [6J and rendered visible under an electron microscope [71.
The substrate specificity [81 and the function of neuraminidase [91 are particularly interesting. Studies o n the in-vitro
interactions between cell receptor and virus neuraminidase
represent the starting point for the elucidation of the mechanism of infection by myxoviruses.
Lecture at Giessen on October 21, 1969 [VB 215 IE]
German version: Angew. Chem. 82, 48 (1970)
[*I Prof. Dr. R. Drzeniek
Institut fur Virologie der Universitat
63 Giessen, Frankfurter Strasse 87 (Germany)
[I] K . Repke, Der Internist 7, 418 (1966).
[2] M . K . Jain, A . Strickholm, and E. H . Cordes, Nature (London) 222, 871 (1969).
[3] W. Weidel, Annu. Rev. Microbiol. 12, 27 (1958).
[4] E . Klenk, Hoppe-Seylers Z . physiol. Chem. 268, 50 (1941).
[5] A . Gottschafk: Glycoproteins. Their Composition, Structure
and Function. Elsevier, Amsterdam 1966.
[6] R . Drzeniek, J . T . Sefo, and R . Rott, Biochirn. biophysica
Acta 128, 547 (1966).
[7] R . Drzeniek, H . Frank, and R . Rott, Virology 36, 703 (1968).
[8] R . Drzeniek, Biochem. biophysic. Res. Commun. 26, 631
(1967).
[9] J . T. Sefo and R . Rott, Virology 30, 731 (1966).
By R. Drzeniek [*I
Cell receptors pIay a decisive roIe in many interesting
biological phenomena, e . g . in the action of drugs, toxins,
hormones, antibodies, and viruses o n living cells. Although
the best-known receptor theory, that proposed by Paul Ehrlich who regarded cell receptors as having defined chemical
structures, dates back to about 1900, first attempts to isolate
these receptors and t o characterize them chemically were
not made until comparatively recently.
Angew. Chem. internat. Edit.
/ Vol. 9
(1970)
1 No. I
Organometal Pseudohalides 111
By K. Dehniekec*]
Lewis acids and alkyl- and arylmetal compounds react with
gaseous CIN3 to form organometal azides in accordance with
equation (1).
R n M t ClN3 +- Rn-lM-N3+
RCl
(1)
79
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