[ccp4bb] AW: [ccp4bb] emergency substitute for RT loop cover?

[Herman . Schreuder]

You might try some shrink-wrap. 
Herman


-Ursprüngliche Nachricht-
Von: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] Im Auftrag von Keller, 
Jacob
Gesendet: Montag, 7. Juli 2014 18:43
An: CCP4BB@JISCMAIL.AC.UK
Betreff: Re: [ccp4bb] emergency substitute for RT loop cover?

Anyone ever tried a glob of paratone-n for this? I remember it being good for 
keeping crystals happy during Xe derivatization, but that was for a relatively 
short time. If this is at the synchrotron, the dataset would only take a few 
minutes at most, so maybe it would work.

JPK

-Original Message-
From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Frank von 
Delft
Sent: Monday, July 07, 2014 12:33 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: [ccp4bb] emergency substitute for RT loop cover?

Hi all

Pretend you were stuck having to do RT data collection but without access to 
either Mitegen MicroRT Capillaries or the more old-fashioned quartz 
capillaries, to pop over the loop.

Anybody have suggestions of alternative ways of doing this?  I do want to use 
loops (I never learnt how to suck up crystals in capillaries).

I have access to a passably stocked biochemistry teaching lab, and could at a 
pinch go rifle some more advanced research labs.  (No, I'm not at home ;)

Thanks!
phx

[ccp4bb] off topic: Crystallization robots

[Scott Pegan]

In the process of acquiring a crystallography robot for the laboratory.  I
have narrowed along capability and budgetary constraints to either an
Formulatrix NT8, or a Art Robbins Gryphon.  I know the Art Robbins
instrument characteristics pretty well, does anyone have any
experience/advice on the NT8?

Scott

[ccp4bb] Gentle reminder, early Bird Registration deadline ICCBM15 in Hamburg

[mesters]

Gentle reminder, early bird registrations deadline, July 15th, is 
approaching fast.


Students, postdocs and scientists interested in the latest 
crystal-growth methodologies and advances in serial crystallography, 
neutron diffraction and other exciting techniques may wish to *join 
ICCBM15* (Sep. 17 - 20, Hamburg, www.iccbm15.org).


As far as the *pre-conference workshop* is concerned (consisting of 
short presentations, practical demonstrations and hands-on exercises 
taught by an international team of experts), the number of free places 
for students and postdocs is steadily decreasing, so better sign up 
sooner than later.



Chairpersons: Christian Betzel and Jeroen Mesters

[ccp4bb] WG: Murnau conference on Structural Biology

[Clemens Steegborn]

 

Dear colleagues,

 

I would like to remind you that registration for the Murnau conference on
Structural Biology will end soon (July 31st). At the meeting from September
10 to 13, we will have eminent scientist as speakers from various fields of
structural biology (see http://www.murnauconference.de/2014/schedule.html
for the program), and there are several additional slots for oral
presentations that will be filled through selection from the submitted
abstracts. 

 

For more information on this meeting please have a look at 

http://www.murnauconference.de/2014/

 

I'm looking forward to meeting you in Murnau!

 

With best regards

Clemens

 


---

Prof. Dr. Clemens Steegborn 

University of Bayreuth 

Dept. Biochemistry, NW III
Universitaetsstr. 30
95447 Bayreuth, Germany

 

phone: ++49 0921 / 55 - 7831

fax: ++49 0921 / 55 - 7832

email:   
clemens.steegb...@uni-bayreuth.de

web: 
www.biochemie.uni-bayreuth.de

 

 

[ccp4bb] question about powder diffraction

[Kianoush Sadre-Bazzaz]

Hi 

If a sample of powder crystal (say Nickel) is shot with monochromatic x-rays, 
one will observe reflections from planes that satisfy Bragg's Law. For Ni the 
first four planes are (111, 200, 202, 311) with 2theta (44, 52, 76, 93 degrees) 
respectively. 

 Why doesn't one observe a reflection at, say, 45 degrees? There will be a 
grain oriented in the powder such that x-rays reflect at 45 degrees and so 
forth. I would expect a continuum of reflections...

thanks for the insight.

Kianoush

Re: [ccp4bb] question about powder diffraction

[Edward A. Berry]

The plane will scatter, and all atoms in the plane will scatter in phase
if angle of incidence equals angle of reflection. this is how a mirror
reflects. Furthermore all the parallel planes will also reflect at this angle.
Trouble is the beams scattered from the different parallel planes are
systematically out of phase with each other unless Bragg's law is met
for that set of planes, so interference is destructive and adds up to nothing.
At least that's how I understand it,
eab




On 07/08/2014 03:53 PM, Kianoush Sadre-Bazzaz wrote:

Hi

If a sample of powder crystal (say Nickel) is shot with monochromatic x-rays, 
one will observe reflections from planes that satisfy Bragg's Law. For Ni the 
first four planes are (111, 200, 202, 311) with 2theta (44, 52, 76, 93 degrees) 
respectively.

  Why doesn't one observe a reflection at, say, 45 degrees? There will be a 
grain oriented in the powder such that x-rays reflect at 45 degrees and so 
forth. I would expect a continuum of reflections...

thanks for the insight.

Kianoush

Re: [ccp4bb] question about powder diffraction

[Ian Clifton]

"Edward A. Berry"  writes:

> The plane will scatter, and all atoms in the plane will scatter in phase
> if angle of incidence equals angle of reflection. this is how a mirror
> reflects. Furthermore all the parallel planes will also reflect at this angle.
> Trouble is the beams scattered from the different parallel planes are
> systematically out of phase with each other unless Bragg's law is met
> for that set of planes, so interference is destructive and adds up to nothing.
> At least that's how I understand it,
> eab

Yes, the way I like to think of it as a double condition, the
reflection‐in‐a‐mirror condition *plus* the special condition imposed
by Bragg’s Law. This is why I often prefer the unfashionable spelling
“reflexion”.

-- 
Ian ◎

Re: [ccp4bb] question about powder diffraction

[Ian Tickle]

Yes, the way I like to think of it as a double condition, the

> reflection‐in‐a‐mirror condition *plus* the special condition imposed
> by Bragg’s Law. This is why I often prefer the unfashionable spelling
> “reflexion”.
>
> --
> Ian ◎
>

Me too.  Actually "reflexion" (but the verb is "reflect") is the original
correct spelling (from Latin reflectere & reflexio); apparently at some
point in its history it became misspelt due to a false analogy with
"correct" & "correction" (Latin corrigere & correctio).

Now back to the science!  It's important to understand that a "powder" is
not amorphous which would indeed give a continuous pattern: it's a bunch of
micro-crystals in random orientations.  Therefore a powder diffraction
pattern is a single crystal pattern averaged over all orientations.
Rotating the crystal does not change the Bragg angles of the spots, however
it does change their angular positions so each diffracted beam is smeared
out over conical surface.  Each of these cones then projects as a circle on
a flat area detector (of course in powder diffraction one would use a
linear detector since it's not necessary to measure a complete circle).

Cheers

-- Ian

Re: [ccp4bb] question about powder diffraction

[Boaz Shaanan]

I thought (I think I was told that way early during my PhD studies) that reflexion/reflection is a matter of British/American spelling. In fact Merriam-Webster Dictionary says just
 that:


Definition of REFLEXION

chiefly British variant of reflection 


 and the American Heritage and Oxford dictionaries agree on that too.


 Boaz


 
Boaz Shaanan, Ph.D.

Dept. of Life Sciences  
Ben-Gurion University of the Negev  
Beer-Sheva 84105    
Israel  
    
E-mail: bshaa...@bgu.ac.il
Phone: 972-8-647-2220  Skype: boaz.shaanan  
Fax:   972-8-647-2992 or 972-8-646-1710
 
 








From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Ian Tickle [ianj...@gmail.com]
Sent: Wednesday, July 09, 2014 12:19 AM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] question about powder diffraction




Yes, the way I like to think of it as a double condition, the



reflection‐in‐a‐mirror condition *plus* the special condition imposed
by Bragg’s Law. This is why I often prefer the unfashionable spelling
“reflexion”.

--
Ian ◎




Me too.  Actually "reflexion" (but the verb is "reflect") is the original correct spelling (from Latin reflectere & reflexio); apparently at some point in its history it became misspelt due to a false analogy with "correct" & "correction"
 (Latin corrigere & correctio).


Now back to the science!  It's important to understand that a "powder" is not amorphous which would indeed give a continuous pattern: it's a bunch of micro-crystals in random orientations.  Therefore a powder diffraction pattern is
 a single crystal pattern averaged over all orientations.  Rotating the crystal does not change the Bragg angles of the spots, however it does change their angular positions so each diffracted beam is smeared out over conical surface.  Each of these cones then
 projects as a circle on a flat area detector (of course in powder diffraction one would use a linear detector since it's not necessary to measure a complete circle).


Cheers


-- Ian

Re: [ccp4bb] question about powder diffraction

[Gerard Bricogne]

Dear all,

 The downstream end of this thread seems to have drifted into learned 
considerations of spelling, so I am getting back to this early reply.

 I am surprised that nobody has mentioned the role of the wavelength in
all this: there is no way that one can directly link the first four planes
in a Nickel crystal to a fixed set of 2theta values. The values you quote,
Kianoush, must have been observed for a certain wavelength, but they would
be different for another wavelength. So if you want one of the powder rings
to come out at a 2theta of 45 degrees, adjust the wavelength accordingly so
that Bragg's law be satisfied for the spacing between the corresponding
planes.

 There also seems to be a confusion in the last question (unless I have
completely misunderstood it) about the orientation of a crystal and the
Bragg angle at which it will contribute to the ring pattern of the powder it
belongs to. If there is a crystal oriented with some if its planes at 45
degrees from the X-ray beam, that will simply determine where on each ring
its diffraction spots will contribute: it will have no effect on the Bragg
angles of those spots, that depend purely on the internal spacings between
atoms within the crystal, not on the orientation of the crystal. At the same
wavelength at which you quote the 2theta values for those four rings, the
crystal at 45 degrees from the beam will still have its diffraction spots
contribute to the rings at 44, 52, 76 and 93 degrees.

 Again, forgive me if I have completely misunderstood the initial
question.


 With best wishes,
 
  Gerard.

--
On Tue, Jul 08, 2014 at 04:13:59PM -0400, Edward A. Berry wrote:
> The plane will scatter, and all atoms in the plane will scatter in phase
> if angle of incidence equals angle of reflection. this is how a mirror
> reflects. Furthermore all the parallel planes will also reflect at this angle.
> Trouble is the beams scattered from the different parallel planes are
> systematically out of phase with each other unless Bragg's law is met
> for that set of planes, so interference is destructive and adds up to nothing.
> At least that's how I understand it,
> eab
> 
> 
> 
> 
> On 07/08/2014 03:53 PM, Kianoush Sadre-Bazzaz wrote:
> >Hi
> >
> >If a sample of powder crystal (say Nickel) is shot with monochromatic
x-rays, one will observe reflections from planes that satisfy Bragg's Law.
For Ni the first four planes are (111, 200, 202, 311) with 2theta (44, 52,
76, 93 degrees) respectively. 
> >
> >  Why doesn't one observe a reflection at, say, 45 degrees? There will be
a grain oriented in the powder such that x-rays reflect at 45 degrees and so
forth. I would expect a continuum of reflections...   
> >
> >thanks for the insight.
> >
> >Kianoush
> >

-- 

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