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Re: [ccp4bb]: Data processing
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Carlo,
I put your unit cell through the maXus space group
program. There is the possibility of C-centered monoclinic:
Program o/p:
Unit cell:
a = 89.2110(0.0004) alpha= 90.00(0.000)
b = 89.2140(0.0004) beta = 89.99(0.000)
c = 150.8190(0.0008) gamma= 87.15(0.000)
Niggli reduced cell: 89.211 89.214150.819 90.00 89.99 87.15
Niggli matrix: 7958.6021 7959.1372 22746.3711
0.0000 2.5833 395.3094
Transformation matrix: 1.00 0.00 0.00
0.00 1.00 0.00
0.00 0.00 1.00
Niggli matrix indicates triclinic cell of type P
but ..............................
Checking for higher metric symmetry via LePage method:
Possible 2-Fold Axes - 2-Axis Crit = 0.50, Exp. Error = 0.30 Deg., LATT = P:
Rows Products Angle Between Two Direct Axes
Nr D N Direct Recip Dot Delta 1 2 3 4 5 6 7 8 9
1122.992 2 1 1 0 1 1 0 2 0.000 0. 90. 90.
2129.261 2 1-1 0 1-1 0 2 0.010 90. 0. 90.
3150.819 2 0 0 1 0 0 1 1 0.011 90. 90. 0.
Transformation Matrix: Input (a,b,c) to Conventional Cell(a', b', c'):
(a') ( 1.00-1.00 0.00) (a) (x') ( 0.50-0.50 0.00) (x) Metrically
(b') = ( 1.00 1.00 0.00) (b). (y') = ( 0.50 0.50 0.00) (y). orthorhombic
(c') ( 0.00 0.00 1.00) (c) (z') ( 0.00 0.00 1.00) (z) FOM: 0.011
Latt a b c Alpha Beta Gamma Volume
Input Cell P 89.211 89.214 150.819 90.00 89.99 87.15 1198867.12
Reduc Cell P 89.211 89.214 150.819 90.00 90.01 92.85 1198867.12
Conv. Cell oC 122.992 129.261 150.819 89.99 89.99 90.00 2397734.50 <------- NB
Possible alternative metric symmetry detected.
Chris
===================================================================
Chris Gilmore D.Sc.
Professor of Crystallography
Head of Department
Department of Chemistry
University of Glasgow
Glasgow G12 8QQ, Scotland, UK
Office phone: (44)(0)141 330 3716 Lab phone: (44)(0)141 330 6579
Fax: (44)(0)141 330 4419 email: hod@chem.gla.ac.uk
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> *** CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html ***
>
> On Fri, 30 Mar 2001, Carlo Ciatto wrote:
>
> > Well, it must be triclinic...but the refined cell is the following:
> > 89.211 89.214 150.819 90.000 89.989 87.153 ----> a=b, alpha=beta=90.
> >
>
> Well, it could genuinely be triclinic with two 90.0 degree angles - the
> crystal system only imposes the metric values on the cell parameters -
> they are "necessary but not sufficient"; it's the internal symmetry that
> defines the crystal system (an ultimately space group). Many
> crystallographers who have collected data on more than a few crystals have
> an example of beta = 90.000 for a monoclinic cell, and I'm sure there are
> some out there who have triclinic cells with three 90.00 degree angles.
>
> > Any ideas or suggestions? Where should one look for possible problems or
> > mistakes (before scaling)? I must confess my unease with symmetry, maybe
> > the Denzo table is showing me something that I cannot see.
> >
>
> Something to look for would be incorrect main beam position. Have a look
> at the images and see if there is apparent symmetry of intensities with
> the indices shifted by + or - 1.
>
> Other things could be high absorption coupled with a badly centred
> crystal.
>
> Harry
> --
> Dr Harry Powell, MRC Laboratory of Molecular Biology, MRC Centre, Hills
> Road, Cambridge, CB2 2QH
>
>