The new experiment types MXPressP and MXPressP_SAD (Pseudo helical) operate in much the same way as the usual automated workflows on MASSIF-1 in that all the current features are retained, such as resolution selection, strategy input, diffraction volume calculation and smart beam sizing; but the strategy for a complete data set is divided over a number of positions with a full dose for each position. We are, for the moment, remaining cautions and a full 'complete' data set is first collected from the best volume. The reason for this is two fold: 1. We have seen that crystal heterogeneity can often lead to a number of the partial data sets being of varying quality and 2. We are eager to compile a large amount of data on how and when helical data collection is superior to single position.

Contact Matthew Bowler for help.

The new workflow is fully described in the following publication. Please cite if you found MXPressP useful.

Svensson, O., Gilski, M., Nurizzo, D. & Bowler, M. W. (2018). Multi-position data collection and dynamic beam sizing: recent improvements to the automatic data-collection algorithms on MASSIF-1, Acta Cryst. D74, 433-440

Pseudo-helical data collection proceeds as follows:

1. Please select MXPressP or MXPressP_SAD in the 'experiment type' field for the required samples in ISPyB. Please also add other requirements if needed, such as required beam diameter, already observed resolution etc.., as for other workflows.

2. A specified number of positions can be given, however, if left blank the default is 5 (1 single data collection and 4 partial).

3. At the mesh scan stage the number of positions is automatically detected, positions must be within 30% of the value of position 2. Peaks that will overlap in omega are also eliminated. Therefore, the number of positions used can vary depending on the quality and orientation of the crystal.

Figure 1. Detection of positions within a crystal. In this case 10 positions were requested and located.

4. Once centred, 4 characterisation images are collected from the best position. A strategy is then calculated for a complete data set and the the data collected. As usual, in case of indexing failure, a default data collection of 180º is collected (240º for triclinic and 360º for SAD data collection).

5. Once completed, a strategy is then calculated to collect a complete data set from the N positions determined in the mesh scan that are within 30% of the value of position 2. The strategy, as usual, accounts for the volume of the positions, beam diameter etc. Again, in case of a failure in indexing, default data collections are performed at each position using a full dose and the rotation range determined by 180º/N (240º/N for triclinic and 360º/N for SAD). Each partial data set has a 5º overlap with the next to assist with scaling.

6. At the end of the workflow one complete data set and N partial data sets will have been collected. Auto processing will run on all data sets but at the moment does not merge the partial data sets. We hope to have this implemented in the near future.

Examples:

1. Orthorhombic native, 5 positions detected, beam diameter automatically adjusted to 100 µm:

Single position:

sub-| Phi  |Rot.  | Exposure| N.of||Over|sWedge|Exposure|Exposure| Dose  | Dose  |Comple-
We-|start |width | /image  | ima-||-lap| width| /sWedge| total  |/sWedge| total |teness
dge|degree|degree|     s   |  ges||    |degree|   s    |   s    | MGy   |  MGy  |  %
----------------------------------||-----------------------------------------------------
1    84.00   0.10     0.230  1300|| No  130.00    299.1    299.1   3.940   3.940   99.9

Pseudo helical data collection on 4 subsequent positions:

   Wedge number =   1 Crystal position =  1
1    84.00   0.10     0.772   350|| No   35.00    270.1    270.1   3.559   3.559   72.0
Wedge number =   2 Crystal position =  2
1   119.00   0.10     0.772   350|| No   35.00    270.1    270.1   3.559   3.559   73.8
Wedge number =   3 Crystal position =  3
1   154.00   0.10     0.772   350|| No   35.00    270.1    270.1   3.559   3.559   87.0
Wedge number =   4 Crystal position =  4
1   189.00   0.10     0.772   350|| No   35.00    270.1    270.1   3.559   3.559  100.0

2. Tetragonal Se-Met SAD, 5 positions detected, beam diameter automatically adjusted to 50 µm:

Single position:

----------------------------------||-----------------------------------------------------
sub-| Phi  |Rot.  | Exposure| N.of||Over|sWedge|Exposure|Exposure| Dose  | Dose  |Comple-
We-|start |width | /image  | ima-||-lap| width| /sWedge| total  |/sWedge| total |teness
dge|degree|degree|     s   |  ges||    |degree|   s    |   s    | MGy   |  MGy  |  %
----------------------------------||-----------------------------------------------------
1     0.00   0.10     0.041  3600|| No  360.00    146.3    146.3   9.183   9.183  100.0
-----------------------------------------------------------------------------------------

Pseudo-helical collection on 4 subsequent positions:

----------------------------------||-----------------------------------------------------
sub-| Phi  |Rot.  | Exposure| N.of||Over|sWedge|Exposure|Exposure| Dose  | Dose  |Comple-
We-|start |width | /image  | ima-||-lap| width| /sWedge| total  |/sWedge| total |teness
dge|degree|degree|     s   |  ges||    |degree|   s    |   s    | MGy   |  MGy  |  %
----------------------------------||-----------------------------------------------------
Wedge number =   1 Crystal position =  1
1     0.00   0.10     0.082   900|| No   90.00     74.1     74.1   4.653   4.653   99.9
Wedge number =   2 Crystal position =  2
1    90.00   0.10     0.082   900|| No   90.00     74.1     74.1   4.653   4.653  100.0
Wedge number =   3 Crystal position =  3
1   180.00   0.10     0.082   900|| No   90.00     74.1     74.1   4.653   4.653  100.0
Wedge number =   4 Crystal position =  4
1   270.00   0.10     0.082   900|| No   90.00     74.1     74.1   4.653   4.653  100.0
-----------------------------------------------------------------------------------------