Heavy-atom method - Revision history

BrianMcMahon: Added German and Spanish translations (U. Mueller)

2017-11-14T09:19:48Z

Added German and Spanish translations (U. Mueller)

BrianMcMahon: Style edits to align with printed edition

2017-05-15T13:55:36Z

Style edits to align with printed edition

MassimoNespolo: languages

2016-03-30T11:22:49Z

languages

AndreAuthier at 05:24, 4 April 2008

2008-04-04T05:24:42Z

BrianMcMahon at 11:06, 3 April 2008

2008-04-03T11:06:03Z

BrianMcMahon at 09:41, 3 April 2008

2008-04-03T09:41:27Z

New page

An application of [[Patterson methods]] in crystal [[structure determination]]. For a compound containing a heavy atom (''i.e.'' one with a significantly higher [[atomic scattering factor]] than the others present) the diffraction phases calculated from the position of the heavy atom are used to compute a first approximate [[electron density map]]. Further portions of the structure are recognisable as additional peaks in the map. Successive approximate electron density maps may then be calculated to solve the entire structure.

== Discussion ==

[[Image:sfac4.gif|right]]

The figure shows how the [[structure factor]] is derived by vector addition of the scattered waves from the different contributing atoms in the unit cell. Consider the case of an atom with a very much higher scattering factor than any of the others (<math>f_{0} >> \sum_{i} f_i</math>); it is clear that the total phase angle <math>\phi</math> will be small, and that the net phase of the structure factor differs very little from that of the heavy-atom component alone.

If the positions of known heavy atoms can be determined in this way, then the Patterson

← Older revision		Revision as of 09:19, 14 November 2017
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−	<~~Font~~ color="blue">Méthode de l'atome lourd</~~Font~~> (''Fr''). <~~Font~~ color="black">Metodo dell'atomo pesante</~~Font~~> (''It''). <~~Font~~ color="purple">重原子法</~~Font~~> (''Ja'').	+	<font color="blue">Méthode de l'atome lourd</font> (''Fr''). <font color="red">Schweratom-Methode</font> (''Ge''). <font color="black">Metodo dell'atomo pesante</font> (''It''). <font color="purple">重原子法</font> (''Ja''). <font color="green">Método del átomo pesado</font> (''Sp'').

	An application of [[Patterson methods]] in crystal [[structure determination]]. For a compound containing a heavy atom (''i.e.'' one with a significantly higher [[atomic scattering factor]] than the others present) the diffraction phases calculated from the position of the heavy atom are used to compute a first approximate [[electron density map]]. Further portions of the structure are recognisable as additional peaks in the map. Successive approximate electron density maps may then be calculated to solve the entire structure.		An application of [[Patterson methods]] in crystal [[structure determination]]. For a compound containing a heavy atom (''i.e.'' one with a significantly higher [[atomic scattering factor]] than the others present) the diffraction phases calculated from the position of the heavy atom are used to compute a first approximate [[electron density map]]. Further portions of the structure are recognisable as additional peaks in the map. Successive approximate electron density maps may then be calculated to solve the entire structure.

← Older revision		Revision as of 13:55, 15 May 2017
Line 1:		Line 1:
−	<Font color="blue">Méthode de l'atome lourd</Font> (''Fr''); <Font color="black">Metodo dell'atomo pesante</Font> (''It''); <Font color="purple">重原子法</Font> (''Ja'').	+	<Font color="blue">Méthode de l'atome lourd</Font> (''Fr''). <Font color="black">Metodo dell'atomo pesante</Font> (''It''). <Font color="purple">重原子法</Font> (''Ja'').
−

	An application of [[Patterson methods]] in crystal [[structure determination]]. For a compound containing a heavy atom (''i.e.'' one with a significantly higher [[atomic scattering factor]] than the others present) the diffraction phases calculated from the position of the heavy atom are used to compute a first approximate [[electron density map]]. Further portions of the structure are recognisable as additional peaks in the map. Successive approximate electron density maps may then be calculated to solve the entire structure.		An application of [[Patterson methods]] in crystal [[structure determination]]. For a compound containing a heavy atom (''i.e.'' one with a significantly higher [[atomic scattering factor]] than the others present) the diffraction phases calculated from the position of the heavy atom are used to compute a first approximate [[electron density map]]. Further portions of the structure are recognisable as additional peaks in the map. Successive approximate electron density maps may then be calculated to solve the entire structure.

← Older revision		Revision as of 11:22, 30 March 2016
Line 1:		Line 1:
−	<Font color="blue"> Méthode de l'atome lourd </Font> (''Fr'').	+	<Font color="blue">Méthode de l'atome lourd</Font> (''Fr''); <Font color="black">Metodo dell'atomo pesante</Font> (''It''); <Font color="purple">重原子法</Font> (''Ja'').
		+

	An application of [[Patterson methods]] in crystal [[structure determination]]. For a compound containing a heavy atom (''i.e.'' one with a significantly higher [[atomic scattering factor]] than the others present) the diffraction phases calculated from the position of the heavy atom are used to compute a first approximate [[electron density map]]. Further portions of the structure are recognisable as additional peaks in the map. Successive approximate electron density maps may then be calculated to solve the entire structure.		An application of [[Patterson methods]] in crystal [[structure determination]]. For a compound containing a heavy atom (''i.e.'' one with a significantly higher [[atomic scattering factor]] than the others present) the diffraction phases calculated from the position of the heavy atom are used to compute a first approximate [[electron density map]]. Further portions of the structure are recognisable as additional peaks in the map. Successive approximate electron density maps may then be calculated to solve the entire structure.

← Older revision		Revision as of 05:24, 4 April 2008
Line 1:		Line 1:
		+	<Font color="blue"> Méthode de l'atome lourd </Font> (''Fr'').
		+
	An application of [[Patterson methods]] in crystal [[structure determination]]. For a compound containing a heavy atom (''i.e.'' one with a significantly higher [[atomic scattering factor]] than the others present) the diffraction phases calculated from the position of the heavy atom are used to compute a first approximate [[electron density map]]. Further portions of the structure are recognisable as additional peaks in the map. Successive approximate electron density maps may then be calculated to solve the entire structure.		An application of [[Patterson methods]] in crystal [[structure determination]]. For a compound containing a heavy atom (''i.e.'' one with a significantly higher [[atomic scattering factor]] than the others present) the diffraction phases calculated from the position of the heavy atom are used to compute a first approximate [[electron density map]]. Further portions of the structure are recognisable as additional peaks in the map. Successive approximate electron density maps may then be calculated to solve the entire structure.

@@ Line 5: / Line 5: @@
 [[Image:sfac4.gif|right]]
-The figure shows how the [[structure factor]] is derived by vector addition of the scattered waves from the different contributing atoms in the unit cell. Consider the case of an atom with a very much higher scattering factor than any of the others (<math>f_{0} >> \sum_{i} f_i</math>); it is clear that the total phase angle <math>\phi</math> will be small, and that the net phase of the structure factor differs very little from that of the heavy-atom component alone.
+The figure shows how the [[structure factor]] is derived by vector addition of the scattered waves from the different contributing atoms in the unit cell. Consider the case of an atom with a very much higher scattering factor than any of the others <math>(\,\,f_0 >> \sum_i f_i \,\,)</math>; it is clear that the total phase angle <math>\phi</math> will be small, and that the net phase of the structure factor differs very little from that of the heavy-atom component alone.
-If the positions of known heavy atoms can be determined in this way, then the Patterson
+If the positions of known heavy atoms can be determined in this way, then the Patterson map, which describes interatomic vectors, allows  nearby peaks to be assigned to other atoms in accordance with expected molecular geometry. These are then used in calculating phase angles for the next approximate electron density map.